Consider investigating The Maze
During the congestion control and vanguards-lite deployments in 0.4.7, we managed to disturb some balrogs in Tor's circuit construction maze: #40612 (closed) and #40603 (closed).
In the first case, The Maze was managing to build 4 hop exit circuits somehow. This should not be happening, and can degrade performance if these circuits are used for website activity. Very oddly, these circuits managed to get built primarily when Tor is being used only as a Bridge, with no direct client or onion service activity.
In the second case, Tor was failing to find a valid 2nd hop for its path, briefly, during startup.
A brave soul could try to investigate these. This is not worth a ton of effort, but perhaps during conflux or UDP implementation we will uncover the secrets of whatever trap doors there are in the Maze that cause this activity.
To do so, we will have to use Info logs to keep an eye out for those two logs, since they have been demoted. This ticket is to remind us to at least check if we can get them to happen in sims/testing.