Demos are 100% guaranteed to imperceptibly desync and I don't know why

Even playing back a demo you literally just recorded can do this. I have no idea why. It was all working a year ago, and now everything is pain and I don't know why. I wanted the "BAD DEMO!!" message to mean something, but it... very much doesn't at the moment, lmao.

Does anyone have an example demo for 2.2.4 where the game give the BAD DEMO message? None of the demos I've recorded recently have done this, though I haven't recorded many admittedly.

(Basically I intend to have a look into this issue at last, since no one else has until now)

assigned to @MonsterIestyn

A replay that (at least for me) consistently desynchs. Recorded just now as of writing.

It seems to occur with the crawlas specifically... MAP01-guest.lmp

thx this definitely gives what I'm looking for, I noticed it pops up the moment you actually get hurt by one of them which may be a clue

quick question, actually, did you actually get hurt by one of the crawlas at around 0:22 in your original play?

no

hm okay, that's interesting then

Here's another one. It may be related to the player moving at high speeds...

MAP01-guest.lmp

Speed does seem to play a role in this desynch...

MAP01-guest.lmp

This one seems to have desynched for unknown reasons, however...

MAP01-guest.lmp

thanks, that should be plenty for me to test for now

For those who didn't see my notes in Discord last night, this is what I've found so far:

• Sometimes, a blue Crawla might not see the player on demo playback, even though it saw the player when the demo was first recorded. This somehow leads to all the other crawlas going out of sync eventually (for reasons I have not determined yet, probably due to random seed being different)
• A possible culprit is validcount, which is used to indicate if lines, etc have already been looked at during a search. This is just a guess of mine though, based on the fact that P_CheckSight uses it.

mentioned in issue #250

Has the changes to increased locational precision for players in replays fixed this issue? Or is the validcount non-wiping still a concern?

No idea if anything has changed since a year ago tbh, I haven't looked into this issue since then.