End portal caused crash playing existing 1.12.2 game

Playing an existing single player survival 1.12.2 game in 1.13.

Went to an End portal that was already active.

Jumped in. Landed on the floor below instead of tp to the End.

I could walk around in the portal, jump back in etc for about 30 seconds.

Then the game froze and eventually crashed. No crash report was created.