I’ll mention some things. Jottacloud changed authentication, but Duplicati’s partial fix is pending, however this other thread is suffering from a different error. Jottacloud support for us is limited.
There’s also a Duplicati workaround there using rclone which also seems to be glitching with Jottacloud.
Implement exponential backoff for backend errors #4661 is another option so far just in Canary releases which you may or may not want to use for serious work, as Canary can add bugs along with good things.