All the rooms had history visibility enabled, so it sounds like something might have been going wrong there on your homeserver. In terms of membership changes

All the rooms had history visibility enabled, so it sounds like something might have been going wrong there on your homeserver. In terms of membership changes being ratelimited - yes, this is an anti-abuse mechanism, and the default synapse config is overly conservative. We don't have a way of overriding that globally though, and the FOSDEM use case of loads of rooms flying around meant some people fell over it a bunch. Sorry you got bitten by this.