First Thermal Dyanmics, now FastCraft corrupts my world (one world each). :p Got a crash on flatworld (overworld settings) testmap, using FTBInfinity, and Fastcraft 1.19. I flew to the edge of the loaded chunks where I had a FunkyLocomotion frame quarry system going. It's a conspiracy against the frame quarries I tell 'ya!
One thing that I did do was disable the Witchcraft mod after loading the world. I've noticed a few mods tend to crash if you load up chunks that had old data in it (I think Journey Map is one of those?).