[Samsung Galaxy A3, A5, A7 (2017) Questions & Answe] diaboliquenoodlesfig:
After rebooting my A5 2017 a few days ago, it seems to have some problems. It does "boot" fine, asks for my (encryption) password, and goes to the "starting phone..." screen.

After this the screen goes blank. Pressing the power button once doesn't do anything. Holding the power button shows a screen with the options: lockdown (doesn't work), power off and restart.

It does not show my launcher nor anything else, just those lockdown, poweroff and restart button.

-------- beginning of system
E vold : Failed to chmod /data/system_ce/0: No such file or directory
E vold : Failed to chmod /data/misc_ce/0: No such file or directory
E vold : Failed to chmod /data/media/0: No such file or directory
E StorageManagerService: No valid MediaStore provider found
<>
TaskPersister: restoreTasksForUserLocked: Unable to list files from /data/system_ce/0/recent_tasks
BackupPasswordManager: Unable to read backup pw version
BackupPasswordManager: Unable to read saved backup pw hash
--------- beginning of kernel

After which this stands out to me (removed a whole lot of "yunk"):

<>
W vold : Trim failed on /data: Inappropriate ioctl for device
W vold : Failed to open none: No such file or directory
<>
--------- beginning of crash
F libc : Fatal signal 6 (SIGABRT), code -1 (SI_QUEUE) in tid 4119 (main), pid 4119 (main)
F libc : crash_dump helper failed to exec
E [3: kworker/3:2: 2713] cnss_wlan_unregister_oob_irq_handler: no OOB task is running
E [3: kworker/3:2: 2713] wlan_platform_sdio_enumerate: notify_func=ffffffc000818658, mmc_host_dev=ffffffc0b94ca818, device_present=0
E : [3: kworker/3:2: 2713] card removed
E [0: kworker/u16:3: 1448] mmc1: card remove detected
E [0:iptables-restor: 3899] audit: rate limit exceeded
--------- beginning of main
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E CarrierIdProvider: read carrier list from ota pb failure: java.io.FileNotFoundException: /data/misc/carrierid/carrier_list.pb: open failed: ENOENT (No such file or directory)
<>
E rkstack.proces: failed to connect to jdwp control socket: Connection refused
E com.android.se: failed to connect to jdwp control socket: Connection refused
E m.android.phon: failed to connect to jdwp control socket: Connection refused
E ndroid.setting: failed to connect to jdwp control socket: Connection refused
< above multiple times >
E StorageSessionController: Failed to exit session: emulated;0. Killing MediaProvider...
E StorageSessionController: com.android.server.storage.StorageSessionController$ExternalStorageServiceException: Failed to end session: [SessionId: emulated;0. UpperPath: /storage/emulated. LowerPath: /data/media
<>
E StorageManagerService: Failed to mount volume VolumeInfo{emulated;0}:
E StorageManagerService: type=EMULATED diskId=null partGuid= mountFlags=PRIMARY|VISIBLE
E StorageManagerService: mountUserId=0 state=CHECKING
E StorageManagerService: fsType=null fsUuid=null fsLabel=null
E StorageManagerService: path=/storage/emulated internalPath=/data/media
E StorageManagerService:
E StorageManagerService: com.android.server.storage.StorageSessionController$ExternalStorageServiceException: Failed to start session: [SessionId: emulated;0. UpperPath: /storage/emulated. LowerPath: /data/media]
<>
E StorageUserConnection: Service: [ComponentInfo{com.android.providers.media.module/com.android.providers.media.fuse.ExternalStorageServiceImpl}] is null. User [0]
<>
E StorageManagerService: Failed to notify volume state changed to the Storage Service
E StorageManagerService: com.android.server.storage.StorageSessionController$ExternalStorageServiceException: Failed to notify volume state changed for vol : StorageVolume: Internal shared storage
< All StorageManagerService/StorageUserConnection error's above multiple times>
F zygote64: jni_internal.cc:729] JNI FatalError called: (com.android.providers.media.module) frameworks/base/core/jni/com_android_internal_os_Zygote.cpp:786: Failed to mount /data_mirror/data_de/null/0/com.google.android.gms to /data/user_de/0/com.google.android.gms: No such file or directory
F zygote64: runtime.cc:655] Runtime aborting...
F zygote64: runtime.cc:655] Dumping all threads without mutator lock held
<>
E libc : failed to raise ambient capability 0: Operation not permitted
E libc : failed to raise ambient capability 1: Operation not permitted
< Above repeated but then number increases >
E DEBUG : failed to readlink /proc/6117/fd/0: Permission denied
E DEBUG : failed to readlink /proc/6117/fd/1: Permission denied
< Above repeated but then number increases >
F crash_dump64: crash_dump.cpp:474] failed to attach to thread 6117, already traced by 0 ()
E libprocessgroup: Error encountered killing process cgroup uid 10187 pid 6108: Permission denied
< A lot repeated errors of the Permission/denied and operation not permitted above + the StorageManagerService/StorageUserConnection errors >

Based on those errors, I think my /data partition is broken. However, when booting into TWRP recovery, the partition looks fine and I can browse all the files?

ROM: official lineageOS

Please let me know if you know how to fix this, or how to troubleshoot further. It's luckily not my main phone, but I'd like it to be usable again.