Size is not an error in itself, but seeing the same Size (size of the upload being done by the put operation) and Hash (mathematical computation as an additional check on file integrity) five times in a row is worrying because it could be that default –number-of-retries (with a new name for each try) to upload kept on failing.
What storage type is this, did it work before, and does it offer any logs that would give a view from its end?
Duplicati is not good at pointing one to the exact log, but can you also look at Job → Show log → General and About → Show log → Stored for anything at the right time. If not, you might need to do a run to watch About → Show log → Live → Retry, or (if nothing else reveals what went wrong), set up an actual log file.