[G3 Q&A, Help & Troubleshooting] swallowtail23:
Some more troubleshooting.

Trying to mount manually in terminal in TWRP gives me a mount unknown error 150.

Running a non-invasive e2fsck gives me:

e2fsck 1.41.14 (22-Dec-2010)
Warning: skipping journal recovery because doing a read-only filesystem check.
Pass 1: Checking inodes, blocks, and sizes
Inode 7, i_size is 3082895360, should be 3087097856. Fix? no

Inode 245415, i_blocks is 704, should be 712. Fix? no

Deleted inode 261925 has zero dtime. Fix? no

Pass 2: Checking directory structure
Entry 'net.dinglisch.android.taskerm' in /data (244801) references inode 342934 found in group 42's unused inodes area.
Fix? no

Entry 'net.dinglisch.android.taskerm' in /data (244801) has deleted/unused inode 342934. Clear? no

Entry 'base.apk' in /app/net.dinglisch.android.taskerm-1 (342899) references inode 342932 found in group 42's unused inodes area.
Fix? no

Entry 'base.apk' in /app/net.dinglisch.android.taskerm-1 (342899) has deleted/unused inode 342932. Clear? no

Entry 'lib' in /app/net.dinglisch.android.taskerm-1 (342899) references inode 342933 found in group 42's unused inodes area.
Fix? no

Entry 'lib' in /app/net.dinglisch.android.taskerm-1 (342899) has deleted/unused inode 342933. Clear? no

Entry 'net.dinglisch.android.taskerm' in /dalvik-cache/profiles (1020002) references inode 1020523 found in group 125's unused inodes area.
Fix? no

Entry 'net.dinglisch.android.taskerm' in /dalvik-cache/profiles (1020002) has deleted/unused inode 1020523. Clear? no

Entry 'data@app@net.dinglisch.android.taskerm-1@base.apk@classes.dex' in /dalvik-cache/arm (1020003) references inode 1020522 found in group 125's unused inodes area.
Fix? no

Entry 'data@app@net.dinglisch.android.taskerm-1@base.apk@classes.dex' in /dalvik-cache/arm (1020003) has deleted/unused inode 1020522. Clear? no

Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Inode 244801 ref count is 227, should be 226. Fix? no

Inode 342899 ref count is 3, should be 2. Fix? no

Pass 5: Checking group summary information
Block bitmap differences: -(1389467--1390267) -3348514
Fix? no

Free blocks count wrong for group #25 (293, counted=292).
Fix? no

Free blocks count wrong for group #37 (4806, counted=4853).
Fix? no

Free blocks count wrong for group #42 (20629, counted=19028).
Fix? no

Free blocks count wrong (5806109, counted=5471235).
Fix? no

Inode bitmap differences: -261925 -(342932--342935) -(1020522--1020523)
Fix? no

Free inodes count wrong for group #32 (7338, counted=7337).
Fix? no

Free inodes count wrong for group #42 (7950, counted=7945).
Fix? no

Directories count wrong for group #42 (57, counted=58).
Fix? no

Free inodes count wrong for group #125 (7639, counted=7637).
Fix? no

Free inodes count wrong (1692439, counted=1689847).
Fix? no

/dev/block/mmcblk0p43: ********** WARNING: Filesystem still has errors **********

/dev/block/mmcblk0p43: 4841/1697280 files (8.7% non-contiguous), 988001/6794110 blocks

Parted gives me this:

Model: MMC SDW32G (sd/mmc)
Disk /dev/block/mmcblk0: 31.3GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number Start End Size File system Name Flags
1 16.8MB 83.9MB 67.1MB fat16 modem
2 83.9MB 84.9MB 1049kB sbl1
3 84.9MB 85.5MB 524kB dbi
4 85.5MB 86.0MB 524kB DDR
5 86.0MB 88.1MB 2097kB aboot
6 88.1MB 89.1MB 1049kB rpm
7 89.1MB 90.2MB 1049kB tz
8 90.2MB 90.2MB 4096B pad
9 90.2MB 91.2MB 1049kB sbl1b
10 91.2MB 91.8MB 524kB dbibak
11 91.8MB 92.8MB 1049kB rpmbak
12 92.8MB 93.9MB 1049kB tzbak
13 93.9MB 94.9MB 1049kB rpmf
14 94.9MB 95.9MB 1049kB tzf
15 95.9MB 96.5MB 524kB sdif
16 96.5MB 98.6MB 2097kB abootf
17 98.6MB 101MB 2093kB spare1
18 101MB 117MB 16.8MB boot
19 117MB 151MB 33.6MB ext4 persist
20 151MB 168MB 16.8MB recovery
21 168MB 171MB 3146kB modemst1
22 171MB 174MB 3146kB modemst2
23 174MB 174MB 4096B pad1
24 174MB 177MB 3146kB fsg
25 177MB 178MB 524kB fsc
26 178MB 178MB 524kB ssd
27 178MB 178MB 4096B pad2
28 178MB 179MB 524kB encrypt
29 179MB 179MB 524kB eksst
30 179MB 179MB 8192B rct
31 179MB 185MB 5226kB spare2
32 185MB 201MB 16.8MB misc
33 201MB 235MB 33.6MB laf
34 235MB 268MB 33.6MB fota
35 268MB 285MB 16.8MB spare3
36 285MB 294MB 8389kB ext4 drm
37 294MB 302MB 8389kB ext4 sns
38 302MB 336MB 33.6MB ext4 mpt
39 336MB 369MB 33.6MB factory
40 369MB 2533MB 2164MB ext4 system
41 2533MB 3171MB 638MB ext4 cache
42 3171MB 3439MB 268MB ext4 cust
43 3439MB 31.3GB 27.8GB ext4 userdata
44 31.3GB 31.3GB 513kB grow