I have had this issue before for a temporary time but when i updated my mac it seemed to fix the problem, although a Roblox studio update could've also been the reason for that as well. Anyways the issue started when i was typing into a script and out of no where it began to lag behind very severely until it was virtually impossible to code. I temporarily fixed the problem once again by un-parenting the script from the script editor window and finally i could type without lag. But then my studio started crashing/being extremely slow and taking 5-10 mins to play or test the game every time or it would crash either before or after pressing Stop. I tried turning all of the Graphic and Editor Quality levels all the way down to 01 and changed my graphics mode to Direct3D11 and i have uninstalled and reinstalled Roblox Studio several times and nothing seems to be working?