[Galaxy S 4 i9505 Android Development] grandoth:
To follow up on this for more data points:

1. I Odined back to stock, and came all the way back. Same issue.

2. I manually formatting the partitions with terminal in TWRP with the below. Same issue.

mkfs.f2fs /dev/block/mmcblk0p##

3. I temporarily switched to [JDCTeam][5.1.1][17 August] Optimized CyanogenMod 12.1 builds to test F2FS. All of the /system, /cache, and /data partitions remained as F2FS! While I am still getting similar errors for /cache and /data, they ultimately mount as F2FS. /system appears just fine. Logcat below:

<3>EXT4-fs (mmcblk0p16): VFS: Can't find ext4 filesystem

<3>EXT4-fs: failed_mount

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/system,target=/system,type=ext4)=-1

<7>SELinux: initialized (dev mmcblk0p16, type f2fs), uses xattr

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/system,target=/system,type=f2fs)=0

<3>fs_mgr: mount_with_alternatives(): Mounted /dev/block/platform/msm_sdcc.1/by-name/system on /system with fs_type=f2fs instead of ext4

<7>SELinux: initialized (dev mmcblk0p1, type vfat), uses mountpoint labeling

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/apnhlos,target=/firmware,type=vfat)=0

<7>SELinux: initialized (dev mmcblk0p2, type vfat), uses mountpoint labeling

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/mdm,target=/firmware-mdm,type=vfat)=0

<6>fs_mgr: check_fs(): mount(/dev/block/platform/msm_sdcc.1/by-name/efs,/efs,ext4)=-1

<6>fs_mgr: Running /system/bin/e2fsck on /dev/block/platform/msm_sdcc.1/by-name/efs

<6>e2fsck: e2fsck 1.42.9 (28-Dec-2013)

<6>e2fsck: /dev/block/platform/msm_sdcc.1/by-name/efs: recovering journal

<6>e2fsck: /dev/block/platform/msm_sdcc.1/by-name/efs: clean, 51/880 files, 1134/3488 blocks

<6>EXT4-fs (mmcblk0p10): mounted filesystem with ordered data mode. Opts: noauto_da_alloc,journal_async_commit,errors=panic

<7>SELinux: initialized (dev mmcblk0p10, type ext4), uses xattr

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/efs,target=/efs,type=ext4)=0

<3>EXT4-fs (mmcblk0p18): VFS: Can't find ext4 filesystem

<3>EXT4-fs: failed_mount

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/cache,target=/cache,type=ext4)=-1

<6>fs_mgr: Running /system/bin/fsck.f2fs -f /dev/block/platform/msm_sdcc.1/by-name/cache

<6>fsck.f2fs: Info: Force to fix corruption

<6>fsck.f2fs: Info: sector size = 512

<6>fsck.f2fs: Info: total sectors = 4239360 (in 512 bytes)

<6>fsck.f2fs: Info: MKFS version

<6>fsck.f2fs: "Linux version 3.4.107-cyanogenmod-g1541b49 (antaresone@JDCTeam-Build02) (gcc version 4.8 (GCC) ) #1 SMP PREEMPT Tue Jun 23 01:01:50 CEST 2015"

<6>fsck.f2fs: Info: FSCK version

<6>fsck.f2fs: from "Linux version 3.4.108-Alucard-PWR-CORE (b--b@JDCTeam) (gcc version 4.9.x-sabermod 20150804 (release) (SaberMod-JDCTeam-4.9.4_Cortex_A15) ) #1 SMP PREEMPT Sun Aug 16 19:11:33 CEST 2015"

<6>fsck.f2fs: to "Linux version 3.4.108-Alucard-PWR-CORE (b--b@JDCTeam) (gcc version 4.9.x-sabermod 20150804 (release) (SaberMod-JDCTeam-4.9.4_Cortex_A15) ) #1 SMP PREEMPT Sun Aug 16 19:11:33 CEST 2015"

<6>fsck.f2fs:

<6>fsck.f2fs: [FSCK] Unreachable nat entries [Ok..] [0x0]

<6>fsck.f2fs: [FSCK] SIT valid block bitmap checking [Ok..]

<6>fsck.f2fs: [FSCK] Hard link checking for regular file [Ok..] [0x0]

<6>fsck.f2fs: [FSCK] valid_block_count matching with CP [Ok..] [0x92]

<6>fsck.f2fs: [FSCK] valid_node_count matcing with CP (de lookup) [Ok..] [0xc]

<6>fsck.f2fs: [FSCK] valid_node_count matcing with CP (nat lookup) [Ok..] [0xc]

<6>fsck.f2fs: [FSCK] valid_inode_count matched with CP [Ok..] [0x9]

<6>fsck.f2fs: [FSCK] free segment_count matched with CP [Ok..] [0x3f7]

<6>fsck.f2fs: [FSCK] next block offset is free [Ok..]

<6>fsck.f2fs: [FSCK] fixing SIT types

<6>fsck.f2fs: [FSCK] other corrupted bugs [Ok..]

<6>fsck.f2fs:

D/qdutils ( 198): DEBUG_CALC_FPS: 0

D/qdutils ( 198): period: 10

D/qdutils ( 198): ignorethresh_us: 500000

<6>fsck.f2fs: Done.

<7>SELinux: initialized (dev mmcblk0p18, type f2fs), uses xattr

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/cache,target=/cache,type=f2fs)=0

<3>fs_mgr: mount_with_alternatives(): Mounted /dev/block/platform/msm_sdcc.1/by-name/cache on /cache with fs_type=f2fs instead of ext4

<3>EXT4-fs (mmcblk0p29): VFS: Can't find ext4 filesystem

<3>EXT4-fs: failed_mount

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/userdata,target=/data,type=ext4)=-1

<6>fs_mgr: Running /system/bin/fsck.f2fs -f /dev/block/platform/msm_sdcc.1/by-name/userdata

<6>synaptics_rmi4_i2c 3-0020: synaptics_init_power_on: until lcd does not turn on.

<6>max77693-muic max77693-muic: func:max77693_muic_usb_detect info->muic_data->sw_path:0

<6>synaptics_rmi4_i2c 3-0020: synaptics_init_power_on: until lcd does not turn on.

<6>[SSP]: MSG From MCU - Init

<6>Gyro Temp Init

<6>CheckLightLux Init

<6>AD 6 1 0 1

<6>[SSP]: debug_work_func(1) - Sensor state: 0x3fff, RC: 0, MS: 0

<6>synaptics_rmi4_i2c 3-0020: synaptics_init_power_on: until lcd does not turn on.

<6>fsck.f2fs: Info: Force to fix corruption

<6>fsck.f2fs: Info: sector size = 512

<6>fsck.f2fs: Info: total sectors = 20439040 (in 512 bytes)

D/libEGL ( 423): loaded /vendor/lib/egl/libEGL_adreno.so

<6>fsck.f2fs: Info: MKFS version

<6>fsck.f2fs: "Linux version 3.4.107-cyanogenmod-g1541b49 (antaresone@JDCTeam-Build02) (gcc version 4.8 (GCC) ) #1 SMP PREEMPT Tue Jun 23 01:01:50 CEST 2015"

<6>fsck.f2fs: Info: FSCK version

<6>fsck.f2fs: from "Linux version 3.4.108-Alucard-PWR-CORE (b--b@JDCTeam) (gcc version 4.9.x-sabermod 20150804 (release) (SaberMod-JDCTeam-4.9.4_Cortex_A15) ) #1 SMP PREEMPT Sun Aug 16 19:11:33 CEST 2015"

<6>fsck.f2fs: to "Linux version 3.4.108-Alucard-PWR-CORE (b--b@JDCTeam) (gcc version 4.9.x-sabermod 20150804 (release) (SaberMod-JDCTeam-4.9.4_Cortex_A15) ) #1 SMP PREEMPT Sun Aug 16 19:11:33 CEST 2015"

<6>fsck.f2fs: [FIX] (fsck_chk_orphan_node: 926) --> Discard orphan inodes: ino [0xc85]

<6>fsck.f2fs:

<6>fsck.f2fs: NID[0xc85] is unreachable

<6>fsck.f2fs: [FSCK] Unreachable nat entries [Fail] [0x1]

<6>fsck.f2fs: [FSCK] SIT valid block bitmap checking [Fail]

<6>fsck.f2fs: [FSCK] Hard link checking for regular file [Ok..] [0x0]

<6>fsck.f2fs: [FSCK] valid_block_count matching with CP [Fail] [0x2c900]

<6>fsck.f2fs: [FSCK] valid_node_count matcing with CP (de lookup) [Fail] [0x935]

<6>fsck.f2fs: [FSCK] valid_node_count matcing with CP (nat lookup) [Ok..] [0x936]

<6>fsck.f2fs: [FSCK] valid_inode_count matched with CP [Fail] [0x89c]

<6>fsck.f2fs: [FSCK] free segment_count matched with CP [Ok..] [0x1152]

<6>fsck.f2fs: [FSCK] next block offset is free [Ok..]

<6>fsck.f2fs: [FSCK] fixing SIT types

<6>fsck.f2fs: [FSCK] other corrupted bugs [Fail]

<6>fsck.f2fs:

<6>fsck.f2fs: Done.

<7>SELinux: initialized (dev mmcblk0p29, type f2fs), uses xattr

<6>fs_mgr: __mount(source=/dev/block/platform/msm_sdcc.1/by-name/userdata,target=/data,type=f2fs)=0

<3>fs_mgr: mount_with_alternatives(): Mounted /dev/block/platform/msm_sdcc.1/by-name/userdata on /data with fs_type=f2fs instead of ext4