[HTC 10 Questions & Answers] Zekoslawen:
Have a 64GB HTC 10 which was OTAed from stock Nougat to Oreo. Unlocked bootloader, installed TWRP, rooted with Magisk, then followed the guide in https://xdaforums.com/t/solution-no...-0-to-nougat-7-0.3748999/page-2#post-75580986 to downgrade with S-ON to 7.0 which I have on my older HTC 10 (which is 32GB storage and has a dead SD card slot). Now the 64GB phone is working well, except it's only showing 32GB storage.

I ran into some small problems when flashing the Nougat RUU. The first time I tried with fastboot as per instructions and got this error

user# md5sum "2PS6IMG_PERFUME_UHL_N70_SENSE80GP_MR_HTC_Europe_2.41.401.41_Radio_1.0.U010241a@61226_79.07_F_release_507791_signed_2_4.zip" | grep 5736b58742eed2df0272f10605bfa7ae
5736b58742eed2df0272f10605bfa7ae 2PS6IMG_PERFUME_UHL_N70_SENSE80GP_MR_HTC_Europe_2.41.401.41_Radio_1.0.U010241a@61226_79.07_F_release_507791_signed_2_4.zip
user# fastboot oem rebootRUU
OKAY [ 0.024s]
Finished. Total time: 0.024s
user# fastboot flash zip "2PS6IMG_PERFUME_UHL_N70_SENSE80GP_MR_HTC_Europe_2.41.401.41_Radio_1.0.U010241a@61226_79.07_F_release_507791_signed_2_4.zip"
Invalid sparse file format at header magic
error: write_sparse_skip_chunk: don't care size 876597310 is not a multiple of the block size 4096
Sending sparse 'zip' 1/2 (1048572 KB) error: write_sparse_skip_chunk: don't care size 876597310 is not a multiple of the block size 4096
error: write_sparse_skip_chunk: don't care size 876597310 is not a multiple of the block size 4096
OKAY [ 38.306s]
Writing 'zip' (bootloader) HOSD CL#1012001
(bootloader) ERR lzipv2_init : Cannot open file /dev/fastboot_download_Z
(bootloader) CSUg7
(bootloader) ERR [SD_UPDATE_ERR] update_fb_ZIP_buf: can not find ZIP hea
(bootloader) der
(bootloader) ERR [SD_UPDATE_ERR] sddownload failed: 22
(bootloader) ERR Update zip file failed.
(bootloader) ERR ZIP ERROR, exit read zip loop
(bootloader) ERR ZIP signature checking failed...
(bootloader) Update zip file OK
(bootloader) ERR ZIP ERROR CODE, 22
(bootloader) end@Done
FAILED (remote: '22 RU_HEADER_ERROR ')
fastboot: error: Command failed
user#

So I flashed from SD card per HTCdev instructions and got the expected error the youtuber got before flashing hosd (I think it was error 12). After flashing hosd and flashing RUU again twice from SD card, both times I got the same error: tp_SYN3708.img@FAIL, 33 RU_UPDATE_FIRMWARE_FAIL, but the process was apparently completed

Recovery was broken so had to reflash TWRP, and then did the persist erasure and then the phone booted in Nougat successfully.

It shows the same old IMEI and serial, recognizes SIM, SD card, Wifi, Bluetooth, headphones and speakers working. The only thing I can see wrong is it now shows 32GB internal storage instead of 64GB.

old fastboot getvar all on Oreo:

(bootloader) kernel: lk
(bootloader) product: htc_pmeuhl
(bootloader) version: 1.0
(bootloader) max-download-size: 1578400000
(bootloader) serialno: ...
(bootloader) slot-count: 0
(bootloader) current-slot:
(bootloader) imei: ...
(bootloader) version-main: 3.16.401.2
(bootloader) boot-mode: download
(bootloader) version-baseband: 2.0.U010241a@71204
(bootloader) version-bootloader: 1.0.0.000
(bootloader) mid: 2PS620000
(bootloader) cid: HTC__034

fastboot getval all after finishing the flashing process, with Nougat:

(bootloader) kernel: lk
(bootloader) product: htc_pmeuhl
(bootloader) version: 1.0
(bootloader) max-download-size: 1579200000
(bootloader) serialno: ...
(bootloader) current slot:
(bootloader) imei: ...
(bootloader) version-main: 2.41.401.41
(bootloader) version-baseband: 1.0.U010241a@61226
(bootloader) version-bootloader: 1.0.0.000
(bootloader) mid: 2PS620000
(bootloader) cid: HTC__034

Any ideas how to fix this? It's not a big deal since I've got a massive SD card but wbn to use the full internal storage :)