S3 backups - no errors but no success either - bucket permissions?

I've got a newly setup staging server using Virtualmin and I'm fiddling with getting S3 backup happening. I've got it configured (I believe) correctly.

• Listing the available buckets works
• I can create a new bucket from the Virtualmin interface
• If I click on the newly created bucket (in VirtualMin) I can see its properties (after waiting about 30 seconds for it to have a think)
• if I click on any of the existing buckets in the list it thinks forever

Is this an S3 permission thing? I have no idea where to start looking.

If I attempt to run a backup against any existing bucket (not created inside VirtualMin) then it just runs forever and uses a ton of CPU. No errors are produced but it never completes. The server itself has one test domain on it with a handful of small files, so I would expect the process to be fairly quick.

Backups against the a bucket created by VirtualMin actually do work!

thanks! Chris

Operating system CentOS Linux 7.6.1810 Virtualmin 6.06