You won鈥檛 see any files on the Nextcloud Android app. It doesn鈥檛 matter if you have a new connected account or an already connected account.
After a few seconds/minutes the error message below appears
3 Android devices have this error, 2 iOS devices run without problems
No but strangely enough I have this behavior on 3 other instances running on v20
Nextcloud version: 20.0.0.9
Operating system and version: Debian 10
Apache or nginx version: nginx/1.18.0
PHP version: 7.4
************ CAUSE OF ERROR ************
java.util.ConcurrentModificationException
at java.util.ArrayList.sort(ArrayList.java:1472)
at java.util.Collections.sort(Collections.java:206)
at com.owncloud.android.utils.FileSortOrderByName.sortCloudFiles(FileSortOrderByName.java:52)
at com.owncloud.android.ui.adapter.OCFileListAdapter.swapDirectory(OCFileListAdapter.java:937)
at com.owncloud.android.ui.fragment.OCFileListFragment.listDirectory(OCFileListFragment.java:1275)
at com.owncloud.android.ui.fragment.OCFileListFragment.listDirectory(OCFileListFragment.java:1228)
at com.owncloud.android.ui.fragment.OCFileListFragment.refreshDirectory(OCFileListFragment.java:1224)
at com.owncloud.android.ui.activity.FileDisplayActivity.showFiles(FileDisplayActivity.java:2313)
at com.owncloud.android.ui.activity.DrawerActivity.onNavigationItemClicked(DrawerActivity.java:332)
at com.owncloud.android.ui.activity.DrawerActivity.lambda$null$0$DrawerActivity(DrawerActivity.java:291)
at com.owncloud.android.ui.activity.-$$Lambda$DrawerActivity$GuTM4h_4QmmtMeB02KW202AQU4g.run(Unknown Source:4)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:237)
at android.app.ActivityThread.main(ActivityThread.java:7814)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1075)
************ APP INFORMATION ************
ID: com.nextcloud.client
Version: 30130190
Build flavor: gplay
************ DEVICE INFORMATION ************
Brand: samsung
Device: a50
Model: SM-A505FN
Id: QP1A.190711.020
Product: a50eea
************ FIRMWARE ************
SDK: 29
Release: 10
Incremental: A505FNXXU5BTH8
{"reqId":"Lty38F6YaIRKczNpsl82","level":4,"time":"06.10.2020 13:13:19","remoteAddr":"80.187.106.146","user":"1e9fb3c8-a990-1036-844e-33b12343625b","app":"webdav","method":"PROPFIND","url":"/remote.php/webdav/","message":{"Exception":"TypeError","Message":"Argument 1 passed to OC\\Group\\Manager::getUserGroupIds() must implement interface OCP\\IUser, null given, called in /var/www/DOMAIN/lib/private/Share20/DefaultShareProvider.php on line 884","Code":0,"Trace":[{"file":"/var/www/DOMAIN/lib/private/Share20/DefaultShareProvider.php","line":884,"function":"getUserGroupIds","class":"OC\\Group\\Manager","type":"->"},{"file":"/var/www/DOMAIN/lib/private/Share20/Manager.php","line":1333,"function":"getSharedWith","class":"OC\\Share20\\DefaultShareProvider","type":"->"},{"file":"/var/www/DOMAIN/apps/dav/lib/Connector/Sabre/Node.php","line":323,"function":"getSharedWith","class":"OC\\Share20\\Manager","type":"->"},{"file":"/var/www/DOMAIN/apps/dav/lib/Connector/Sabre/FilesPlugin.php","line":372,"function":"getNoteFromShare","class":"OCA\\DAV\\Connector\\Sabre\\Node","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/PropFind.php","line":96,"function":"OCA\\DAV\\Connector\\Sabre\\{closure}","class":"OCA\\DAV\\Connector\\Sabre\\FilesPlugin","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/DOMAIN/apps/dav/lib/Connector/Sabre/FilesPlugin.php","line":374,"function":"handle","class":"Sabre\\DAV\\PropFind","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"handleGetProperties","class":"OCA\\DAV\\Connector\\Sabre\\FilesPlugin","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/Server.php","line":1063,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/Server.php","line":989,"function":"getPropertiesByNode","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/Server.php","line":1678,"function":"getPropertiesIteratorForPath","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/Server.php","line":1661,"function":"writeMultiStatus","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/CorePlugin.php","line":363,"function":"generateMultiStatus","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"httpPropFind","class":"Sabre\\DAV\\CorePlugin","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/Server.php","line":474,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/Server.php","line":251,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/3rdparty/sabre/dav/lib/DAV/Server.php","line":319,"function":"start","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/apps/dav/appinfo/v1/webdav.php","line":84,"function":"exec","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/DOMAIN/remote.php","line":167,"args":["/var/www/DOMAIN/apps/dav/appinfo/v1/webdav.php"],"function":"require_once"}],"File":"/var/www/DOMAIN/lib/private/Group/Manager.php","Line":325,"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (Android) Nextcloud-android/3.13.1","version":"20.0.0.9"}
I tried a little bit more and it looks like it is a problem when the user comes from LDAP. Local users do not have this problem.
As you can see here it displays the account email strangely

Hello,
I have exactly the same problem on a fresh new NextCloud 20.0 install.
I tested on 2 different phones. While I can see the files on the windows client or on a browser, the Android 3.13.1 shows no files. Pitcures are displayed correctly.
User is coming from LDAP.
In addition to the above, user picture is displayed correctly.
App is not crashing.
Thanks,
Laurent.
ah that's what's happening... ok, I thought I had misconfigured something.
What logs do the developers need?
I have no problem on the web, or with webdav on Joplin. Only the NC Android client can't see any files. It sees activity, and even photos, but no files. I tried resetting data in the app, relogging in, everything. I tried rolling back to an old client and that didn't fix the problem either.
I'm also an LDAP user. NC 20.0
I think this is the same as https://github.com/nextcloud/server/issues/23355
Here's a temporary workaround: https://github.com/nextcloud/server/issues/23355#issuecomment-709477257