Here’s output from logcat:

03-19 16:33:47.099 20119 20119 E AndroidRuntime: FATAL EXCEPTION: main
03-19 16:33:47.099 20119 20119 E AndroidRuntime: Process: android.process.media, PID: 20119
03-19 16:33:47.099 20119 20119 E AndroidRuntime: java.lang.RuntimeException: Unable to start receiver com.android.providers.media.MediaScannerReceiver: java.lang.StringIndexOutOfBoundsException: length=1; index=-3
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.app.ActivityThread.handleReceiver(ActivityThread.java:3619)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.app.ActivityThread.access$1300(ActivityThread.java:237)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1803)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.os.Handler.dispatchMessage(Handler.java:106)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.os.Looper.loop(Looper.java:214)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.app.ActivityThread.main(ActivityThread.java:7078)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at java.lang.reflect.Method.invoke(Native Method)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:964)
03-19 16:33:47.099 20119 20119 E AndroidRuntime: Caused by: java.lang.StringIndexOutOfBoundsException: length=1; index=-3
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at java.lang.String.substring(String.java:1995)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at com.android.providers.media.utils.MPLogger.log(MPLogger.java:118)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at com.android.providers.media.MediaProvider.call(MediaProvider.java:5073)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.content.ContentProvider$Transport.call(ContentProvider.java:403)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.content.ContentResolver.call(ContentResolver.java:1763)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at com.android.providers.media.MediaScannerReceiver.logToDb(MediaScannerReceiver.java:139)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at com.android.providers.media.MediaScannerReceiver.onReceive(MediaScannerReceiver.java:77)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        at android.app.ActivityThread.handleReceiver(ActivityThread.java:3610)
03-19 16:33:47.099 20119 20119 E AndroidRuntime:        ... 8 more

The upload process (I think) then dies:

03-19 16:33:47.164  2044 13653 I ActivityManager: Killing 20133:com.nextcloud.client/u0a0 (adj 100): depends on provider com.android.providers.media/.MediaProvider in dying proc android.process.media (adj 100)