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Tested using g4.11pre-28-g269431575

Using a teleport with the "Actor hits floor" things can crash the game if you enter while jumping into the floor.

From looking at the stack trace, it appears that this particular setup is causing a recursive check due to having "actor hits floor" on both sides of the teleporter, and since the player's Z velocity is non-zero it's running that particular check recursively. Which also causes a massive amount of lag even when it doesn't crash.

Sorry, can't fix without breaking legitimate setups. Doom's teleports are very poorly handled in the engine, i.e. right in the middle of the movement code, which makes them susceptible to such problems