Hello,
Sorry you're running into issues that is a bit unusual. Are you able to provide any additional information about the issue.
Which space had this issue - and which users were trying to access it?
Were these people accessing the space for the first time - and following a join link? Or is this something they have had access to in the past.
If there's an unauthorized message that usually means that one of the AJAX request resulted in a 403. So if possible getting the URL that resulted in the 403 from the network tab would be very helpful for debugging.
Thanks for any help you can provide,
Sean