Thanks for the response. The problem has been happening all week but typically I was able to create a new backup with an additional 20Gb last night. It succeeded without duplicacy exiting. Maybe it was an issue with OneDrive? I’ll keep an eye on it.
After the successful backup I ran a check which is reporting missing chunks for the latest backup. If I look for the missing chunks they are indeed missing from the backup, however, there are ~tmp files with names that match the missing chunk names. I have set the maximum chunk size to 1MB (I’m backing up large files) and the ~tmp file sizes range from 700k-998k so it looks like the upload has stopped before duplicacy can rename the ~tmp file?
It’s a bit worrying that I get a backup successful message when in reality there are issues. I’ll run my next backup with the debug switch and capture the output to a log file to see if it gives any clues. Anything else I can check?