Synchronization failed: `llegalStateException: Duplicate key`

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Describe the bug

Synchronization works initially, but then repeatedly fails. Rich text formatting seemed to initiate the issue, but I'm not sure.

My Nextcloud instance is up and running normally. I can access it via Android or a web browser.

To Reproduce
Steps to reproduce the behavior:

1. Attempt any sync
2. Receive 'Synchronization failed' message.

Expected behavior
Sync as any other app would.

App Version: 4.1.0
App Version Code: 40010090
App Flavor: play

Files App Version Code: 30260090 (PROD)

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OS Version: 4.19.269-g7763b0d7bb61(2023100300)
OS API Level: 33
Device: barbet
Manufacturer: Google
Model (and Product): Pixel 5a (barbet)

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java.lang.IllegalStateException: Duplicate key 590093 (attempted merging values 1 and 2)
	at java.util.stream.Collectors.duplicateKeyException(Collectors.java:133)
	at java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180)
	at java.util.stream.Collectors$$ExternalSyntheticLambda39.accept(Unknown Source:6)
	at java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
	at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1390)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:485)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:475)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:236)
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:517)
	at it.niedermann.owncloud.notes.persistence.NotesRepository.getIdMap(NotesRepository.java:463)
	at it.niedermann.owncloud.notes.persistence.NotesServerSyncTask.pullRemoteChanges(NotesServerSyncTask.java:208)
	at it.niedermann.owncloud.notes.persistence.NotesServerSyncTask.run(NotesServerSyncTask.java:96)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:463)
	at java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1137)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:637)
	at java.lang.Thread.run(Thread.java:1012)

Start by inspecting NotesRepository.getIdMap at line 463, then trace how NotesServerSyncTask.pullRemoteChanges at line 208 uses its result. Reproduce the failure by attempting a sync and determine why duplicate key 590093 reaches this path. Done means synchronization completes without the reported IllegalStateException.