Issues when trying to load a modpack

[Ron_Swansons_Mustache]

So I was playing the Ultra Modded Survival modpack and everything was fine but when I went to go into a different dimension, the window closed and the launcher came back up as if I closed the window. Now when I try to load the modpack, it loads all the way to the main menu then it freezes and the window closes and the launcher comes back up. What's causing this? I have enough ram to run the game so I don't understand what's happening