Deleted events visible in room previews (may be stale room previews in general)

[ara4n]

Description

if the most recent msg gets redacted in a room, you can still see it in the preview text in the room list.

Steps:

1. Enable message previews
2. Send a message "test"
3. Edit the message "test 2"
4. Delete the message

Expected:

The message "test 2" is not displayed in the preview

Observed:

The message "test 2" is displayed in the preview

[t3chguy]

[ara4n]

might be that it was an edited msg that was redacted? or that the user parted the room afterwards?

[t3chguy]

Right with edits that sounds plausible given a redaction doesn't redact the entire edit chain and message previews will fall-through to the latest message they can show

[ara4n]

actually, the problem seems to be that all room previews are very stale for me on Element Nightly version: 2021070403.

the preview for the room i'm currently looking at is currently ~7 messages behind the actual most recent msg in the room.

[ara4n]

This is still happening, and it's really annoying as i just can't trust previews any more.

i think it might be getting stuck after a gappy sync? or if the last message was an edit, it gets confused and doesn't update to the next-best value?

[ara4n]

I just saw this again; this time it was simply that an edited msg appeared in the preview, but as this wasn't the most recent msg in the room, it looked like a bug. However, this doesn't explain the screenshot above, when Erik's msg wasn't an edit; just a stale update. I haven't seen this particular failure mode that recently.

[ara4n]

Just had it again; this time it's not an edited message. It showed the 3rd most recent message as the preview rather than the most recent one.

[germain-gg]

Just had another flavour of this issue

[Johennes]

Reproduced this just now myself.

There seems to be nothing exotic in-between sending the message and redacting it.

[t3chguy]

@Johennes that sounds like #22334

[t3chguy]

Actually that one is a duplicate of this whole issue

[langleyd]

Added repro steps and updated Occurrence. I think at most this falls into the "some users regularly" category.

We should be following the logic of the timeline. I'll have a look and if it's easy to re-use that logic will add a fix.