Ref T8478. I think the cycle is:
- Conpherence Thread > Loads handle for participant > loads file for profile image > loads attached files to check visibility > loads conpherence thread > ...
So, specifically, someone attached their profile image to a thread or message somewhere.
This breaks the cycle by stopping the attached-files visibility check from happening, since we don't need it. This seemed like the easiest link in the chain to break.
Ideally, I think the longer-term and more complete fix here is to stop Conpherence from requiring handles in order to load thread handles (and, generally, having a "handles must not load other handles" rule), but that's not trivial and might not be especially practical.