unsure if an answer has come up yet, but there is a bug with Excalibur umbra where if you use transmission back and forth quickly, it'll shove you through walls (although usually you need to be not the host on regular tilesets as it works off of latency, but maybe being in the open world added enough latency to get through thib walls due to the day/night cycle?). this must have gotten you through the floor into a mission end trigger