[One (M8) Q&A, Help & Troubleshooting] Thijs_Rallye:
Okay, so I dug a little deeper into the OS. I found the console-ramoops which pointed me to the following interesting bit:

[ 9.495655] c2 23 diag: In diag_process_smd_read_data, diag_device_write error: -19
[ 9.829320] c3 457 type=1403 audit(1459234814.406:18): policy loaded auid=4294967295 ses=4294967295
[ 9.869434] c6 487 i2c-msm-v2 78b6000.i2c: i2c_msm_pm_suspend:
[ 10.541031] c6 457 type=1403 audit(1459234815.126:19): policy loaded auid=4294967295 ses=4294967295
[COLOR="DarkRed"][ 10.561355] c1 753 EXT4-fs (mmcblk0p45): warning: mounting fs with errors, running e2fsck is recommended
[ 10.561417] c1 753 blk-core: Attempt to write protected partition mmcblk0p45 block 0
[ 10.561435] c1 753 EXT4-fs (mmcblk0p45): re-mounted. Opts: (null)[/COLOR]
[ 10.580810] c1 271 blk-core: Attempt to write protected partition mmcblk0p45 block 6168
[ 10.580883] c1 271 blk-core: Attempt to write protected partition mmcblk0p45 block 6176
[ 10.580897] c1 271 blk-core: Attempt to write protected partition mmcblk0p45 block 6184
[ 10.580926] c1 271 blk-core: Attempt to write protected partition mmcblk0p45 block 6192
[ 10.580963] c1 754 blk-core: Attempt to write protected partition mmcblk0p45 block 0

Which pointed me to the "partition" mmcblk0p45. So I booted into TWRP recovery and opened up a ADB console window running e2fsck -n -f /dev/block/mmcblk0p45

This gave me the following result:

File /app/CIMEXT9/CIMEXT9.apk (inode #33, mod time Mon Aug 24 09:48:31 2015)
has 2427 multiply-claimed block(s), shared with 1 file(s):
/priv-app/HtcSpeakFull/HtcSpeakFull.apk (inode #3139, mod time Mon Aug 2
4 09:58:49 2015)
Clone multiply-claimed blocks? no
Delete file? no
File /priv-app/HtcSpeakFull/HtcSpeakFull.apk (inode #3139, mod time Mon Aug 24 0
9:58:49 2015) has 2427 multiply-claimed block(s), shared with 1 file(s):
/app/CIMEXT9/CIMEXT9.apk (inode #33, mod time Mon Aug 24 09:48:31 2015)
Clone multiply-claimed blocks? no
Delete file? no
Pass 2: Checking directory structure
Entry 'AntHalService' in /app (12) has an incorrect filetype (was 2, should be 1).
Fix? no
Entry 'BasicDream' in /app (12) has an incorrect filetype (was 2, should be 1).
Fix? no
Entry 'Books' in /app (12) has an incorrect filetype (was 2, should be 1).
Fix? no
Entry '..' in <13>/<15> (15) has an incorrect filetype (was 2, should be 1).
Fix? no
Entry '..' in <17>/<19> (19) has an incorrect filetype (was 2, should be 1).
Fix? no
[COLOR="DarkRed"]Entry 'arm' in /app/Bluetooth (21) has an incorrect filetype (was 2, should be 1).
Fix? no
Entry 'lib' in /app/Bluetooth (21) has an incorrect filetype (was 2, should be 1).
Fix? no[/COLOR]
Entry '..' in <25>/<26> (26) has an incorrect filetype (was 2, should be 1).
Fix? no
Entry 'libbluetooth_jni.so' in <25>/<26> (26) has an incorrect filetype (was 7,should be 1).
Fix? no
Pass 3: Checking directory connectivity
Unconnected directory inode 15 (<13>/<15>)
Connect to /lost+found? no
'..' in ... (15) is <13> (13), should be <The NULL inode> (0).
Fix? no
Unconnected directory inode 19 (<17>/<19>)
Connect to /lost+found? no
'..' in ... (19) is <17> (17), should be <The NULL inode> (0).
Fix? no
Unconnected directory inode 26 (<25>/<26>)
Connect to /lost+found? no
'..' in ... (26) is <25> (25), should be <The NULL inode> (0).
Fix? no
Pass 4: Checking reference counts
Inode 12 ref count is 124, should be 121. Fix? no
Inode 13 ref count is 1, should be 2. Fix? no
Unattached inode 14
Connect to /lost+found? no
Inode 15 ref count is 2, should be 1. Fix? no
Inode 17 ref count is 1, should be 2. Fix? no
Unattached inode 18
Connect to /lost+found? no
Inode 19 ref count is 2, should be 1. Fix? no
Inode 21 ref count is 4, should be 2. Fix? no
Unattached inode 24
Connect to /lost+found? no
Inode 25 ref count is 1, should be 2. Fix? no
Inode 26 ref count is 2, should be 1. Fix? no
Unattached inode 29
Connect to /lost+found? no
Unattached inode 30
Connect to /lost+found? no
Unattached inode 31
Connect to /lost+found? no
Pass 5: Checking group summary information
Block bitmap differences: -(17159--17166) -(17168--17184) -(17208--17452) -1769
1 -(17694--20177) -(20179--27629) -(27631--30471) -(30704--31474)
Fix? no
Free blocks count wrong for group #0 (65064, counted=0).
Fix? no
Free blocks count wrong for group #19 (53167, counted=1).
Fix? no
Free blocks count wrong for group #20 (60520, counted=1).
Fix? no
Free blocks count wrong for group #27 (59167, counted=2498).
Fix? no
Free blocks count wrong for group #31 (23543, counted=32254).
Fix? no
Free blocks count wrong (380522, counted=153815).
Fix? no
Directories count wrong for group #0 (692, counted=686).
Fix? no
/dev/block/mmcblk0p45: ********** WARNING: Filesystem still has errors **********
/dev/block/mmcblk0p45: 4146/262144 files (0.1% non-contiguous), 668054/1048576 blocks

So there is something weird going on in the filesystem. My question is if I can use e2fsck -y /dev/block/mmcblk0p45 without the risk of bricking the device?

Thanks for your replies.

Thijs

TL;DR

: filesystem is partly corrupted, which contains files regarding bluetooth apps. Can I use e2fsck -y /dev/block/mmcblk0p45 without the risk of bricking?