Initial sync included rooms with no information that I'm apparently not in (legacy/unsupported room versions)

[turt2live]

Trying to get members of the room results in name: "M_FORBIDDEN", message: "User @travis:t2l.io not in room !oeCrnyfPhvZiruUJLn:sw1v.org, and room previews are disabled". This is a test room which I should be in.

The room has no name, and I cannot backfill it. 3 of my rooms appear to be impacted by this.

!oeCrnyfPhvZiruUJLn:sw1v.org has the version eventid-noslash-test.
!VXChyxVNCBsWeSGcaN:sw1v.org is state-v2-test (old internal room).
!bNAPsppHlSHCDvMRhh:abolivier.bzh is another test room with a version of org.matrix.msc2260

The theme appears to be that Synapse doesn't recognize the room versions anymore, not that the rooms have reset or been left. Synapse should probably exclude these rooms, or somehow support them enough to refuse new messages?

[clokep]

This sounds like a duplicate of #7083, but with a slightly different failure mode.