S3 sync to BackBlaze no longer working

I have been using backblaze S3 (free 10GB) as my sync target for 6 months without issue. Using multiple Android, windows and linux clients. After I updated yesterday to:

Joplin 2.6.10 (prod, win32)

Client ID: 934a2e3ce27e4140b38601e1d3630c2d
Sync Version: 3
Profile Version: 41
Keychain Supported: Yes

Revision: 98fba37

I have not been able to sync. Checking Sync configuration hangs with "Checking... Please Wait" on every device. Has something changed? Is there a log to check?