500 error when associating Doc with a specific group

Hi, we have an issue with one specific group creating docs.

When a new doc is created, everything seems fine, but on submission, there is a 500 error – in Chrome

“florenceonlineschool.eui.eu is currently unable to handle this request.”

The document is actually created, and shows up in the list of all documents, but not associated with any group – it defaults to a completely public document.

Any attempt to assign the doc to this group gives the same error message.

Other groups are able to create docs fine, and there’s no obvious difference in the settings