I see you received the public mailing of B2 last week :) However, you missed a few important details in it.
BackBlaze B2 added an optional S3 compatibility API in B2 that runs in parallel with the B2 API but does not replace the B2 API. The B2 API continues to function properly. This was communicated to us developers a month in advance, when the S3 compatibility API went live. We did test it but we see no reason to replace our existing B2 API implementation with the S3 compatibility API.
Something else is happening with your backup but without the backup log file I can't tell you what. I do have a suspicion – there was a wrong implementation note in the B2 API about when an upload retry (with a request for a new upload URL) should occur. This is something that we fixed last week but we don't have a public release with that change yet.
Is it possible to ZIP and attach your log file so I can verify this is the case with your backup? Don't worry, attachments are private even in public tickets i.e. only you and our support staff will be able to see them.
Thank you in advance!
Nicholas K. Dionysopoulos
Lead Developer and Director