[One (M7) Q&A, Help & Troubleshooting] alray:
First because the dmesg output is full of errors related to the EMMC:

CMD17 = READ_SINGLE_BLOCK -----> Can't read single block on the EMMC

CMD18 = READ_MULTIPLE_BLOCK ----> Can't read multiple blocks on the EMMC

SD_HW_ERR -----> Basically mean SD HARDWARE ERROR

(...)
(bootloader) [22:57:7.817077] chipset_bootmode(): reset_reason=0x5EA3E3BF
(bootloader) [22:57:7.818538] Board_PID : 232
(bootloader) [22:57:9.187300] [COLOR="Red"][SD_HW_ERR] read data fail in CMD18[/COLOR]
(bootloader) [22:57:9.190050] [COLOR="red"]CMD18: read fifo failed, retry[/COLOR]
(bootloader) [22:57:10.233903] [COLOR="red"][SD_HW_ERR] read data fail in CMD18[/COLOR]
(bootloader) [22:57:10.236825] [COLOR="red"][SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:10.238629] PMIC revision 1: F2
(bootloader) [22:57:10.240348] PMIC revision 2: 9
(bootloader) [22:57:10.243785] MSM?-p?-v1.2(0x2075B0E1) PMIC8038-v2.0
(bootloader) [22:57:10.245564] Gyro ID = 0x69
(bootloader) [22:57:10.247368] Setting gy_type = 1
(bootloader) [22:57:10.251378] reset rt5501 ret 0
(bootloader) [22:57:10.255159] m4_init is finished: 19:49:13, Aug 13 2015
(bootloader) [22:57:10.267861] board_m4 support widevine level 1
(bootloader) [22:57:10.280159] [COLOR="red"][ERR] Cmd18 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:10.284627] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:10.287806] [COLOR="red"][SD_HW_ERR] read data fail in CMD18[/COLOR]
(bootloader) [22:57:10.289439] [COLOR="red"]CMD18: cmd failed[/COLOR]
(bootloader) [22:57:10.292361] [COLOR="red"][SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:10.295024] [COLOR="red"][PG_ERROR] htc_pg_hdr_get(117):[22:57:10.2[/COLOR]
(bootloader) 97001] [COLOR="red"]sd_read_sector error[/COLOR]
(bootloader) [22:57:10.300094] [COLOR="red"][PG_ERROR] htc_pg_part_hdr_get(169):[22:57[/COLOR]
(bootloader) :10.302156] [COLOR="red"]htc_pg_hdr_get failed[/COLOR]
(bootloader) [22:57:10.307484] radio_update_drm_config: read pg2fs_wvkey_
(bootloader) lv1 len (0) failed
(bootloader) [22:57:10.309975] valid keybox is not existed
(bootloader) [22:57:10.323601] [COLOR="red"][ERR] Cmd18 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:10.328069] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:10.331248] [COLOR="red"][SD_HW_ERR] read data fail in CMD18[/COLOR]
(bootloader) [22:57:10.332881] [COLOR="red"]CMD18: cmd failed[/COLOR]
(bootloader) [22:57:10.335803] [COLOR="red"][SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:10.338466] [COLOR="red"][PG_ERROR] htc_pg_hdr_get(117):[22:57:10.3[/COLOR]
(bootloader) [COLOR="red"]40443] sd_read_sector error[/COLOR]
(bootloader) [22:57:10.343536] [COLOR="red"][PG_ERROR] htc_pg_part_hdr_get(169):[22:57[/COLOR]
(bootloader) [COLOR="red"]:10.345598] htc_pg_hdr_get failed[/COLOR]
(bootloader) [22:57:10.350582] radio_update_drm_config: read pg2fs_dpkey
(bootloader) len (0) failed
(bootloader) [22:57:10.362879] [COLOR="red"][ERR] Cmd18 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:10.367347] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:10.370526] [COLOR="red"][SD_HW_ERR] read data fail in CMD18[/COLOR]
(bootloader) [22:57:10.372159] [COLOR="red"]CMD18: cmd failed[/COLOR]
(bootloader) [22:57:10.375080] [COLOR="red"][SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:10.377744] [COLOR="red"][PG_ERROR] htc_pg_hdr_get(117):[22:57:10.[/COLOR]3
(bootloader) [COLOR="red"]79721] sd_read_sector error[/COLOR]
(bootloader) [22:57:10.382814] [COLOR="red"][PG_ERROR] htc_pg_part_hdr_get(169):[22:57[/COLOR]
(bootloader) [COLOR="red"]:10.384876] htc_pg_hdr_get failed[/COLOR]
(bootloader) [22:57:10.389860] radio_update_drm_config: read pg2fs_prkey
(bootloader) len (0) failed
(bootloader) [22:57:10.402111] [COLOR="red"][ERR] Cmd18 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:10.406579][COLOR="red"] [ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:10.409758] [COLOR="red"][SD_HW_ERR] read data fail in CMD18[/COLOR]
(bootloader) [22:57:10.411391] [COLOR="red"]CMD18: cmd failed[/COLOR]
(bootloader) [22:57:10.414312] [COLOR="red"][SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:10.416976][COLOR="red"] [PG_ERROR] htc_pg_hdr_get(117):[22:57:10.4[/COLOR]
(bootloader) 18953][COLOR="red"] sd_read_sector error[/COLOR]
(bootloader) [22:57:10.422046][COLOR="red"] [PG_ERROR] htc_pg_part_hdr_get(169):[22:57[/COLOR]
(bootloader) :10.424108] [COLOR="red"]htc_pg_hdr_get failed[/COLOR]
(bootloader) [22:57:10.428834] radio_update_drm_config: read pg2fs_prkey
(bootloader) data failed
(bootloader) [22:57:10.442460] [COLOR="red"][ERR] Cmd18 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:10.446928] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:10.450108] [COLOR="red"][SD_HW_ERR] read data fail in CMD18[/COLOR]
(bootloader) [22:57:10.451740] [COLOR="red"]CMD18: cmd failed[/COLOR]
(bootloader) [22:57:10.454662][COLOR="red"] [SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:10.457326][COLOR="red"] [PG_ERROR] htc_pg_hdr_get(117):[22:57:10.4[/COLOR]
(bootloader) 59302] [COLOR="red"]sd_read_sector error[/COLOR]
(bootloader) [22:57:10.462395][COLOR="red"] [PG_ERROR] htc_pg_part_hdr_get(169):[22:57[/COLOR]
(bootloader) :10.464457] htc_pg_hdr_get failed
(bootloader) [22:57:10.469269] isGDriveRedeemed: read pg2fs_gdvoucher_red
(bootloader) eemed failed
(bootloader) [22:57:10.473222] chipset_bootmode(): reset_reason=0x5EA3E3B
(bootloader) F
(bootloader) [22:57:10.481127] radio_boot_mode() poweron_status=0x0000002
(bootloader) 0, reset_reason=0x5EA3E3BF, hw_reason=0x00000000
(bootloader) [22:57:10.483877] enter recovery_offmod_charging
(bootloader) [22:57:10.486283] SecuritySDInit counter = 1
(bootloader) [22:57:10.490407] [SD_ERR] The project does not support SD c
(bootloader) ard
(bootloader) [22:57:10.491696] 902910 902E20
(bootloader) [22:57:10.704671] <0>No USB device attached, portsc 0x8C0010
(bootloader) 00
(bootloader) [22:57:10.706819] <1>usbhost_start failed
(bootloader) [22:57:10.807104] 902910 902E20
(bootloader) [22:57:10.898336] usb_init_hw: pull low d+
(bootloader) [22:57:10.930685] No smart SD in device disable detect
(bootloader) [22:57:10.933950] [JAVACARD_ERR] SD/USBDISK Init error
(bootloader) [22:57:10.935755] ARM11 Boot Mode: 22
(bootloader) [22:57:10.937645] Platform: HBOOT-8930
(bootloader) [22:57:10.969198] [COLOR="red"][ERR] Cmd17 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:10.973666] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:10.976845] [COLOR="red"][SD_HW_ERR] read data fail in CMD17[/COLOR]
(bootloader) [22:57:10.978478][COLOR="red"] CMD17: cmd failed[/COLOR]
(bootloader) [22:57:10.981399] [COLOR="red"][SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:10.984922] [COLOR="red"][ERR] partition_read_emmc(876): error 2[/COLOR]
(bootloader) [22:57:10.996460] [COLOR="red"][ERR] Cmd17 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:11.000928] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:11.004107] [COLOR="red"][SD_HW_ERR] read data fail in CMD17[/COLOR]
(bootloader) [22:57:11.005740] [COLOR="red"]CMD17: cmd failed[/COLOR]
(bootloader) [22:57:11.008661][COLOR="red"] [SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:11.012184] [COLOR="red"][ERR] partition_read_emmc(876): error 2[/COLOR]
(bootloader) [22:57:11.016051] [ERR] Boot/Recovery image does not exist!!
(bootloader) !
(bootloader) [22:57:11.085061] [COLOR="red"][ERR] Cmd18 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:11.089529] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:11.092708] [COLOR="red"][SD_HW_ERR] read data fail in CMD18[/COLOR]
(bootloader) [22:57:11.094341] [COLOR="red"]CMD18: cmd failed[/COLOR]
(bootloader) [22:57:11.097262] [COLOR="red"][SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:11.099926][COLOR="red"] [PG_ERROR] htc_pg_hdr_get(117):[22:57:11.1[/COLOR]
(bootloader) 01903] [COLOR="red"]sd_read_sector error[/COLOR]
(bootloader) [22:57:11.104996] [COLOR="red"][PG_ERROR] htc_pg_part_hdr_get(169):[22:57[/COLOR]
(bootloader) :11.107058] htc_pg_hdr_get failed
(bootloader) [22:57:11.119953] [COLOR="red"][ERR] Cmd17 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:11.124421] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:11.127600][COLOR="red"] [SD_HW_ERR] read data fail in CMD17[/COLOR]
(bootloader) [22:57:11.129232] [COLOR="red"]CMD17: cmd failed[/COLOR]
(bootloader) [22:57:11.132154] [COLOR="red"][SD_HW_ERR] SD: Read data fail..[/COLOR]
(bootloader) [22:57:11.136192] [FAT_ERROR] fat_open_file: load bpb fail(-
(bootloader) 5)
(bootloader) [22:57:11.140403] No RADIOVER.CFG in radio image for SSD ver
(bootloader) sion!
(bootloader) [22:57:11.152260][COLOR="red"] [ERR] Cmd17 polling status timed out, MCI_[/COLOR]
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:11.156728] [COLOR="red"][ERR] sdcc_command: sdcc_poll_status error[/COLOR]
(bootloader) , rc: 2
(bootloader) [22:57:11.159907][COLOR="red"] [SD_HW_ERR] read data fail in CMD17[/COLOR]
(bootloader) [22:57:11.161540] [COLOR="red"]CMD17: cmd failed[/COLOR]
(bootloader) [22:57:11.164461] [SD_HW_ERR] SD: Read data fail..
(bootloader) [22:57:11.168500] [COLOR="red"][FAT_ERROR] fat_open_file: load bpb fail(-[/COLOR]
(bootloader) 5)
(bootloader) [22:57:11.172796] No OPENDSPVER.CFG in adsp image for SSD ve
(bootloader) rsion!
(bootloader) [22:57:11.326390] m4_init_backlight
(bootloader) [22:57:11.444752] m4_battery_stored_data_clean: magic_num=0,
(bootloader) stored_soc=0, stored_ocv=0, stored_cc=0, currtime=ld
(bootloader) [22:57:11.458320] [ERR] Cmd18 polling status timed out, MCI_
(bootloader) STATUS: 0x4C2000
(bootloader) [22:57:11.462788] [ERR] sdcc_command: sdcc_poll_status error
(bootloader) , rc: 2
(bootloader) [22:57:11.465968] [SD_HW_ERR] read data fail in CMD18
(bootloader) [22:57:11.467600] CMD18: cmd failed
(bootloader) [22:57:11.470522] [SD_HW_ERR] SD: Read data fail..
(bootloader) [22:57:11.474044] [ERR] partition_read_emmc(876): error 2
(bootloader) [22:57:11.475505] Start Verify: 3
(bootloader) [22:57:11.487764] [ERR] Cmd25 polling status timed out, MCI_
(bootloader) STATUS: 0x4C0000
(bootloader) [22:57:11.492232] [ERR] sdcc_command: sdcc_poll_status error
(bootloader) , rc: 2
(bootloader) [22:57:11.493349] usb_Vbus 0
(bootloader) [22:57:11.593633] 902910 902E20
(bootloader) [22:57:11.684779] usb_init_hw: pull up d+
(bootloader) [22:57:11.696093]
(bootloader) ###[ Fastboot Mode ]###
(bootloader) [22:57:11.700045] chipset_bootmode(): reset_reason=0x5EA3E3B
(bootloader) F
(bootloader) [22:57:11.701678]
(bootloader) USB_STS_SUSPEND
(bootloader) [22:57:11.791645]
(bootloader) USB_STS_RESET
(bootloader) [22:57:11.793735] USB_SPEED_HIGH
(bootloader) [22:57:11.866477] usb_setupEVICE_WRITE:SET_CONFIGURATION:1
(bootloader) [22:57:11.867938] Set usb_ats = 0
(bootloader) [22:58:50.814885] fastboot_command:[oem dmesg]
(bootloader) [22:58:50.816432] fb_cmd_oem:dmesg
(bootloader) [22:58:50.820728] register_debug_console: new entry ptr=0x90
(bootloader) 000940
(bootloader) [22:59:48.210992] fastboot_command:[oem dmesg]
(bootloader) [22:59:48.212539] fb_cmd_oem:dmesg
(bootloader) [22:59:48.216835] register_debug_console: new entry ptr=0x90
(bootloader) 000940
OKAY [ 1.468s]
finished. total time: 1.468s

Secondly because all fastboot commands requiring to write data on the EMMC are not working:

"fastboot oem lock" ---> Phone will write "HTCL" hex bytes in the pg1fs partition to relock the bootloader ----> Does not work.

"fastboot oem rebootRUU" ----> Phone will write some bytes somewere so the phone know in which mode to reboot ---> Does not work.

While other fastboot commands not requiring to write any data on the EMMC are working, i.e:

fastboot getvar all

fastboot reboot

fastboot oem dmesg

etc etc etc...