Please see your other post Error The base connection is closed for info on debugging upload problems. This post shows the same “The connection was unexpectedly closed.” with a Rename and Retry. While there are workarounds to upload failures (e.g. add retries), bad connections are likely outside Duplicati, which relies on networks to work reasonably well. If files can’t be uploaded, there’s no backup possible.
One Error I see that IS in Duplicati (and found/fixed very recently) is “registering a missing remote file”, which is probably a result of the rename/retry making a dindex file pointing to the original dblock name, before any of the rename/retry work. dblock put retry corrupts dindex, using old dblock name for index – canary regression #3932. Towards the bottom I was trying to get a recovery method for it. Yet unknown.
Regardless, this is a secondary issue from seeming network failures, so please check networks closely.