Upgrading from a 1.0 synapse to the latest causes an issue where the populate_stats_process_rooms background task starts running immediately, however I believe it's actually requiring data that is changed as part of current_state_events_membership to function correctly.

i think there should be a dependency from current_state_events_membership to populate_stats_process_rooms to fix this, but there may also be others - is this something that needs to be thought about when choosing background updates' dependencies, i don't think they automatically wait until the ones from previous versions are run.

This isn't a problem when keeping up to date with synapse, but doing larger bulk updates can cause issues.