In Halo 2 MCC PC, I’ve encountered a bug while using the scarab skull on Cairo Station where if you swap to the plasma rifle and fire it with the skull it crashes MCC and you need to use task manager to close the window.
I’ve been getting this too
Make sure and file a bug report about this on the Halo Support site: https://aka.ms/HaloSupport
Be sure to read over the known issues list first before reporting
I encountered this on Gravemind, Legendary. When the brutes spawn after the brute commander orders the exits to be sealed.