Sync Client (windows) basically stops working since v3.5.2

Ever since I recently upgraded to Client version 3.5.2, it became utterly unusable. On startup, it does actually up/download any changes, but after that, it both fails to notice any change in my local NC folder (even if I force sync), and also it indicates failure to sync whenever there’s changes on the server.

What might be wrong?

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No one has anything relevant to say?..