Linux client syncs external store from NC server again and again

The client is re-syncing a folder (external storage on the server) ever again, restarting from the beginning after a cylcle (of about 20hrs), writing the whole 850 GB. In the process it seems to add hidden copies, each sync more of it, now i ran out of disk space on the client computer.

  • Server and client are running current versions (27.1.3, 3.10.1).
  • I already tried to delete the client sync and re-create it what did not solve the problem.
  • The hidden file copies, created for every file in this directory on the client: