The game crashes when I alt+tab

When I alt+tab out of minecraft, the game crashes. The game will completely freeze, sometimes the music keeps laying, sometimes it doesn't. Sometimes the I get a black screen, sometimes I don't. Sometimes the game will exit by itself, other times I have to close it with task manager. It hasn't done this before and I don't know why it has started. I am using a modded version of the game, Aristois with Optifine version 1.12.2. I usually get 80-90 fps on average with SEUS Ultra shaders. I have tried turning my shaders off, but to no avail. PLS HALP!!!!