These aren't really something personally experienced but I just went
around the codebase looking for all of the Deferred `.callback`,
`.errback`, and `.cancel` and wrapped them with
`PreserveLoggingContext()`
Spawning from wanting to solve
https://github.com/element-hq/synapse/issues/19165 but unconfirmed
whether this has any effect.
To explain the fix, see the [*Deferred
callbacks*](3b59ac3b69/docs/log_contexts.md (deferred-callbacks))
section of our logcontext docs for more info (specifically using
solution 2).
edc0de9fa0