I'm using Joplin right now on my android phone (android 10), and Samsung tablet (android 7). If I choose (in Configuration--> Synchronization-->Synchronization target) for it to sync with "File System", it fails on my android phone(android 10) while succeeds on my tablet(android 7).
(on both devices I've given all the permissions to Joplin.)
--- Does this problem has something to do with android version? ( 7 vs. 10)
Anyway, here's part of the sync report export from my android 7 phone:
12-28T20:07:56,20,"""Error: Error: Could not read directory: /storage/emulated/0/Joplin/locks: Attempt to get length of null array. Path: /storage/emulated/0/Joplin/locks
value@index.android.bundle:1235:313
index.android.bundle:1235:2405
y@index.android.bundle:109:587
index.android.bundle:109:1890
y@index.android.bundle:109:587
o@index.android.bundle:109:1066
index.android.bundle:109:1238
f@index.android.bundle:125:155
index.android.bundle:125:864
y@index.android.bundle:130:581
C@index.android.bundle:130:947
callImmediates@index.android.bundle:130:3004
value@index.android.bundle:27:2919
index.android.bundle:27:1095
value@index.android.bundle:27:2611
value@index.android.bundle:27:1065
value@[native code]
value@[native code]""
12-28T20:07:56,30,"""RevisionService::maintenance: Done in 181ms""
12-28T20:07:56,30,"""RevisionService::collectRevisions: Created revisions for 0 notes""
12-28T20:07:56,30,"""Operations completed: ""
12-28T20:07:56,10,"""Error: Error: Could not read directory: /storage/emulated/0/Joplin/locks: Attempt to get length of null array. Path: /storage/emulated/0/Joplin/locks
value@index.android.bundle:1235:313
index.android.bundle:1235:2405
y@index.android.bundle:109:587
index.android.bundle:109:1890
y@index.android.bundle:109:587
o@index.android.bundle:109:1066
index.android.bundle:109:1238
f@index.android.bundle:125:155
index.android.bundle:125:864
y@index.android.bundle:130:581
C@index.android.bundle:130:947
callImmediates@index.android.bundle:130:3004
value@index.android.bundle:27:2919
index.android.bundle:27:1095
value@index.android.bundle:27:2611
value@index.android.bundle:27:1065
value@[native code]
value@[native code]""
12-28T20:07:56,30,"""MigrationHandler: Acquiring exclusive lock""
12-28T20:07:56,30,"""MigrationHandler: Sync target version is 0 or 1 - creating "locks" and "temp" directory:", "{"version":0}""
12-28T20:07:56,30,"""Sync target is new - setting it up...""
12-28T20:07:56,30,"""Sync target info:", "{"version":0}""
12-28T20:07:56,30,"""Starting scheduled sync""
12-28T20:07:56,30,"""Preparing scheduled sync""
12-28T20:07:56,30,"""Running background sync on timer...""
12-28T20:07:56,30,"""RevisionService::maintenance: Starting...""
12-28T20:07:56,30,"""RevisionService::maintenance: Service is enabled""
12-28T20:02:29,30,"""DecryptionWorker: cannot start because no master key is currently loaded.""
12-28T20:02:28,30,"""Total notes: 5""
12-28T20:02:28,30,"""Total resources: 3""
12-28T20:02:28,20,"""There was some errors:""
12-28T20:02:28,20,"""Error: Error: Directory could not be created. Path: /storage/emulated/0/Joplin/locks
Code: EUNSPECIFIED
value@index.android.bundle:1235:313
index.android.bundle:1235:3439
y@index.android.bundle:109:587
index.android.bundle:109:1890
y@index.android.bundle:109:587
o@index.android.bundle:109:1066
index.android.bundle:109:1238
f@index.android.bundle:125:155
index.android.bundle:125:864
y@index.android.bundle:130:581
C@index.android.bundle:130:947
callImmediates@index.android.bundle:130:3004
value@index.android.bundle:27:2919
index.android.bundle:27:1095
value@index.android.bundle:27:2611
value@index.android.bundle:27:1065
value@[native code]
value@[native code]""