I'm not sure if this is it or not, but I went back, and if I switched parties while NOT on a save marker, I was able to switch parties and complete the pyramid.
If it wasn't "being on the save marker and switching parties" that was causing it, then it has to do with party composition when you split up the teams. I forget the split when I was getting the crash, but the split when I didn't get the crash was:
Team 1: Vahn, Oalston, Siegfried, Nombasu
Team 2: Vera, Elina, Darius, Ami
I also entered the cutscene at the pyramid that leads to the party split/selection, with Vera as my party leader.
No change in version - originally experienced the crash on 1.12, and didn't get the crash on 1.12 and got through the level, and now onto the merged world.