Element blocked on an infinite incremental sync

My EA is locked trying to handle a sync that took forever to process, forcing the app to finaly go in background.

By switching the logs to verbose, I can see that that infinite time is taken by MatrixHQ, trying to process an insane amount of m.room.membership (54k+ in just one log file)

=> Some problem noticed

-> My app can't process the sync, and will then process until the app enters background. Then all is cancelled. When the app will foreground again it will restart to call synapse for the sync/ then start process and fail
=> Infinite loop consume data

Also there is an issue with to_device, they will get re process several times, causing BAD_MAC on EA (and An Olm message got replayed on Element R)