I play in split-screen mode in my world and the second player first entered the nether portal. He was stuck in the loading terrain screen about 5 mins, so I restarted the world. (In that time I have gone through this same nether portal just fine and he wasn't there.) After restart he started suffocating, because portal has led to the same coordinates as in overworld. Next going through portal was just fine. But when he has gone through the end portal it happened again. (World was created in 1.17, so he didn't spawn in void just in blocks)