The e-mail now is correct (with 188.8.131.52?), saying the backup is ok, but indeed tries to put files on GCS (Google Cloud Storage) and receive errors.
Operation Put with file duplicati-bf33e810347ea4a39a5b4a6d979c35ac3.dblock.zip attempt 5 of 5 failed with message: The remote server returned an error: (404) Not Found.
It tries to store the data but receive errors from the server. And doesn’t store anything!
I realize only today, looking in the bucket of GCS, and I have seen that there were no file newer than 8 days ago…