For a site I created in Hub Premium, I can't add community members (from Community Org) into a Core Team. I'm able to log into the Community Org, see members, request to add, but then I get this 512 error. I have an open ticket with Esri Support and the ticket went to internal resources, but it's been a few months and I'm still waiting. Has this happened to anyone before? I think somehow on the back-end, when Hub Premium initiated, there was a disconnect from our Employee Org and our Community Org?
Note: I have admin and elevated privileges for the community member I'm trying to add to the Core Team and the group is not at the group maximum (only 2 existing members in Core team).
Resolution: Esri technical support had to fix the issue on the back-end. They had to correctly re-link our employee org and community org. It's odd that the linkage would be "broken" between the employee org and community org since this gets set-up automatically when you activate Hub Premium, but I guess this happened to us and it was a technical issue bug.