I’v experienced some really weird bugs with replays as well. Yesterday I was playing some really old replays (recorded before 1.16) with my friend. When I hosted a replay, it worked fine. However, after the first replay, my friend hosted one while I was browsing my replay folder in game (via create game menu). After he hosted the replay, I exited the map/replay browser and create game menu via cancel buttons. I joined my friend’s game and we started playing the replay. Everything was just wrong with that replay, map was incorrect and it even had wrong players in it. Terrain was glitched and players in the replay didn’t do much (just moved the workers around a bit).
I belive that the game somehow loaded the map and players from the replay that I had previously selected in the map/replay browser. When I joined my friends replay, it somehow mixed my friend’s replay and my replay together. My friend reported that he didn’t experience this weird bug like I did so it was entirely just on my side.
I took some screenshots:
Terrain is most likely glitched, because the map I had selected was on different tileset.