On the PTR, BuffEnough is currently causing a fatal error during the load screen. I got rid of all my addons except BE and still had the same issue. Turning off BE stopped the fatal errors on load.
This application has encountered a critical error:
Program: C:\Program Files (x86)\World of Warcraft Public Test\Wow.exe
Exception: 0xC0000094 (INT_DIVIDE_BY_ZERO) at 0023:01658DB3