Cannot upload to Amazon S3 after upgrading to Rapid Recovery 6.5

Hi,

after upgrading Rapid Recovery from 6.3 to 6.5.1 i cannot upload an archive to Amazon S3 anymore.

Every time i try to upload i get an Error 400 - Bad Request. The detail view shows the error:

"One or more of the specified parts could not be found. The part may not have been uploaded, or the specified entity tag may not match the part's entity tag."

I tried all types of backup (incremental, delete and replace core), installed the latest agent on the clients, created a completely new archive task, nothing helped.

My Raoid Recovery version is: