Coffee's client failed to encrypt for erdnaxeli

[richvdh]

matrix-org/riot-android-rageshakes#822 has logs from Coffee
https://github.com/matrix-org/riot-web-rageshakes/issues/319 has logs from erdnaxeli

[richvdh]

essentially Coffee's client doesn't seem to know that erdnaxeli is a member of the room

[richvdh]

Interesting to note that erdnaxeli's join event has a topological_ordering of 2780. (Normal topo ordering in this room is up to 16500). Possibly this meant that synapse didn't bother including it in the sync?

[richvdh]

so it looks like matrix.org sent erdnaxeli's HS a list of potential servers which could help with the join; there is no ordering to these, but it looks like it picked darmstadt.ccc.de, which left at topo-ordering 2741.

The use of a server which has left is peculiar, but not necessarily a problem.

[richvdh]

https://github.com/matrix-org/riot-android-rageshakes/issues/832 shows very similar behaviour from @lazz:matrix.org.