"Host not found" with larger number of folders/larger sizes


I’m using nextcloud client for 3 different nextcloud folders. One of them contains a pretty large number of directories (>7000) and quite a bit of data (~600GB). I have seen this before, but this time, it doesn’t go away by itself.
When configuring everything from scratch, it works fine for a while, sometimes it stops working right after restarting the client when all the data was synchronized. If I exclude some larger structure (350GB), it will run fine indefinitely, and as soon as I add it again, the client will stop working at some point. All 3 folders (on different nextcloud installations) will show “No connection to Nextcloud at https://foo. Host foo not found.”
The log file shows:

... desktop-3.5.1/src/gui/folderman.cpp:898 ]:	Run etag job on folder OCC::Folder(0x168c6846e400)
... desktop-3.5.1/src/gui/folderman.cpp:916 ]:	Can not run etag job: Folder is busy

and this will repeat pretty much forever.
I’m running nextcloudclient 3.5.1 from FreeBSD packages. I have had this issue with earlier versions of the client, showing all the same symptoms.
Is there a way to debug this further?