@Tom Wolverson Firstly, apologies for the delay in responding here and any inconvenience this issue may have caused.
If the backup solution modifies the blob multiple times (either with PutBlob, PutBlockList, or other mutation), it will be blocked by design. You don’t want malicious designed or user to accidentally overwrite their backup with encrypted or empty data.
For blockblobs, it typically isn’t necessary to do partial commits with PutBlockList as the temporary block list will last 7 days from the last block written. Some apps still do call PutBlockList with partial data uploaded, but it usually isn’t necessary. The backup app should just put all of the blocks and call PutBlockList once.
Please let us know if you have any further queries. I’m happy to assist you further.
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Please do not forget to and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.