Basically, every so often when fighting with magic, casting the magic can freeze my game. It happens enough to be pretty irritating but how long it takes in between freezes can be entirely random. It's only consistently when I am casting, or have just casted a spell.
I would think that maybe my video card is getting too much pressure on it, but again, this only started after Dragonborn.
I'd like to point out that the spells I use are entirely vanilla. Fireball, Sparks, and Frostbite. I have apocalypse spell package installed, but I don't think I've crashed using one of his spells.