too much recursion in room with old federation backfill

[f0x52]

Describe the bug

The Conduit room backfilled some pretty old messages from July 2024, and this messed with the timeline view in that room, showing only those backfilled messages and loading spinners on either side.
After switching rooms, and refreshing the webapp, nothing seemed to change, but after hitting "mark all as read" and "jump to latest" I got an 'Unexpected Application Error': too much recursion crash.
With a stacktrace that's just _4@https://cinny.staging.pixie.town/assets/index-BXjQ1Mjn.js:103:45929 over and over again
After reloading the room is fine again, and scrolled to the current newest messages.

Reproduction

No response

Expected behavior

No response

Platform and versions

NixOS, Firefox Developer 133.0b1, self-hosted Cinny web v4.4.0, Synapse v1.124.0

Additional context

No response

[f0x52]

Just had the same crash when switching to the Conduit room again, the console shows a bunch of 'Event already in timeline' and then hits too much recursion