I've done some more digging into this on my side yesterday as well. The biggest new piece of information is that rebooting the IDP service seems to have fixed it. I did reboot the entire server after the upgrade, so I'm not sure why one more reboot would make a difference. That said, I did figure out how to capture more details in the logs, so you can see the issue in action.
https://pastebin.com/Bcn4tXq3 - Before Reboot
https://pastebin.com/vXF4p7xH - After Reboot
You can see in both cases Gluu says it's releasing the uid and memberOf attributes, but only in the after reboot example does it show up in the saml response.