Fixed 2.8.0 Members are unable to join groups

With 2.8.0, members are no longer able to join groups. There is no server error generated, however. Instead, when you go to join a group, the following message pops up:

The following error occurred:
Service Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

How many members in the group which you want to join?

This happens when attempting to join any group, whether there are many members or just 2 or 3 members.

This is just a guess, but I suspect it is related to the bug reported in the following thread:

https://nobita.me/threads/2-8-0-fatal-error-when-a-user-sends-in-a-join-request.1520/