room alias lookups on libera.chat timing out

[matrixbot]

This issue has been migrated from #14462.

---

Description

I created a room yesterday, and no client can display it because getting client/v3/directory/room/ times out or crashes with a 502 error.

With curl:

$ curl https://matrix.org/_matrix/client/v3/directory/room/%23valtest8:libera.chat
{"errcode":"M_UNKNOWN","error":"Failed to fetch alias"}

With my own client, the connection times out

And from my browser (regardless of being logged in), I'm getting Cloudflare's 502 Bad Gateway page

Steps to reproduce

• join a room on a different server, with no other user from your own homeserver in the room
• leave and re-join a couple of times
• Eventually the client will be stuck

Homeserver

matrix.org

Synapse Version

1.71.0rc2 (b=matrix-org-hotfixes,39ea774cff,dirty)

Installation Method

No response

Platform

n/a

Relevant log output

n/a

Anything else that would be useful to know?

No response