It looks like if you change the name of a "live" course, which Thinkific lets you do, the new name does not propagate over to the PeerBoard objects, like Group names. The "old" course name is still there, with attached Members, while the "newly renamed course" has to be added manually (create new Group) and then has no Members.
Is it possible that PeerBoard is using the course name instead of some unique course identifier, so that it doesn't auto change when the course name does?
If so, this could cause issues. Course renames are probably rare, but not zero.