Performance on my fairly beefy homeserver was atrocious the last 3-4 days. It took 9 attempts to join the synapse room on Matrix.org, and then the “solution” suggested was to add federation workers. Six hours after I noted more than 85% of my federation traffic was failing 1.37.1 was released, and actually addressed the very issue I was seeing.

If you’re running a Matrix homeserver do yourself, and everyone else, a favor and get off stale releases.

https://matrix.org/blog/2021/06/30/security-update-synapse-1-37-1-released