Failed to find memberships for ["@user:...."] in partial state room !... in the auth events of ["$..."].

[squahtx]

https://sentry.tools.element.io/organizations/element/issues/63004/?project=2&query=is%3Aunresolved

When pushing events in partial state rooms down incremental /sync, we try to find the m.room.member state event for their sender by digging through their auth events, so that we can present the membership to the client. Events usually have a membership event in their auth events, with the exception of the m.room.create event and a user's first join into the room.

When implementing #13477, we forgot to consider the exceptions.

[DMRobertson]

What's the impact of this---does this block incremental syncs?

[squahtx]

Nope, it's just an error-level log message.