Invites are not always included in sync

[schmop]

Description

On fast changing membership states the sync will not reliably include rooms a user was invited to.
It might be related to issues
#4533 and
#4422

Reproduction

This is not easily reproducable, an attempt should look as follows:

• Roomadmin a invites user b into rooms r_a and r_b
• a kicks b from r_a before he accepts the invite
• a changes room_state of r_b multiple times
• b retrieves current rooms via (initial)sync, r_b doesn't show

Version information

We used the synapse version v1.12.0.
Installed per git clone
And is operating in a debian stretch docker container.

Hotfix

A possibility to fix it temporarly is to restart the server or invalidate the caches.

We debugged this issue for quite some time and are using a hotfix, that stops caching from
get_forgotten_rooms_for_user in roommember.py by removing following line:

synapse/synapse/storage/data_stores/main/roommember.py

Line 797 in 9c1b83b

@cached()

[alariej]

It might even be a more general problem. Changes to an invite room do not seem to be included in any sync at all. For example in the case of a "direct" room, no syncs are pushed when the inviter changes display name or avatar, or leaves the room. I tested this with and without lazy_load_members filter parameter, with no difference.

[Barry3D]

I am currently running into this problem with synapse version v1.25.0.

It is easier to reproduce right now:

• User A and B join a room
• User B leaves and forgets the room
• User B closes the client, so that the sync with the invitation isn't immediately pushed
• User A invites User B
• User B opens the client and receives stale data

By looking into the database I found out that the data is received and persisted correctly, however the data in the following syncs only contain the state events for the user leaving the room.

I was also able to fix it via the change suggested in the original issue with slight adjustments since roommember.py has been moved and changed.