tl;dr In multiplayer when you are getting stuck at Waiting For Players after battles, we've found that you can get unstuck by having the attacking, or attacked, player change their UI Theme from the settings menu.

My friends and I have been playing Total War: Warhammer 3 since it released. We love this game! However, multiplayer has consistently had issues where battles will sometimes result in players loading back to the campaign map only for the game to sit, seemingly indefinitely, at Waiting for Players. We tried a lot of things, but the only strategy that had marginal success was letting it sit for 10-20 minutes while we took a break. Sometimes, maybe 10% of the time, we'd come back to the game having progressed to the post battle options.

This also, frustratingly, seems most common in large, or defensive, battles. I'm not sure how many times we've played a fight for 30 minutes, eked out a victory, and then have had the game hang just before the post battle options.

We've been monitoring reddit and the forums, as well as the patch notes, to see if anything ever came up as a solution. Now and then you see someone talking about it, but here we are a few years post release still experiencing it. I had gone so far as to tail the game logs to see if there were any hints there. I don't remember what made me think this, but I thought maybe if there was something to force the UI to reset the game might progress. To see if I could force the game to realize everyone had finished loading I changed Main UI Theme under the game settings, then hit apply, and was instantly met with the Post Battle Options! This seems to get the game unstuck.

We've used this trick consistently ever since and it has worked nearly every time. And when it doesn't, just try again and that gets it. We've not had a case where we couldn't get the game to progress since discovering this.