Sync errors only with some files

I’m using Nextcloud Desktop Client Version 3.8.1 (macOS).

With some files I get sync errors all the time! The error pops up as

some files could not be synced due to errors. See the log for details.

In the desktop client I can only see the alert:

Some files couldn’t be synced.

Somewhere in the client there is a red block with a long message like this:

filepaths is locked.

So at the end I get sync errors but I can’t find any meaningful logs about them. And I have no clue WHY these errors occur and HOW to resolve the issue. I also can’t understand why are the errors happening with some files and not with other files.