What you were expecting to happen, and what actually happened:
Every time I used a fireball scroll or heroism scroll on Sunday (yesterday), it crashed the game right after the rewards screen.
When I rebooted the game, it turned out the scrolls were correctly processed, and the room/floor I used the scroll on was cleared, so I wasn’t cheated in any way that I could see (e.g., the luck scroll I received on the rewards screen was correctly added to my Doom total).
How often does this happen? When did it begin happening?
Every time I used a fireball scroll or a heroism scroll.
Steps to make it happen again
It happened with all three fireball scrolls and with the heroism scroll I used on Sunday. It occurred on floors 26-30 of the Tower of Doom.