So hopefully I can save you some hair pulling because I just figured out how to fix the ‘running out of application memory’ warning that kept popping up while I was working on a project. I assume your computer has plenty enough application memory normally, like mine does, but all of a sudden it starts slowing down, freezing, and that warning pops up.
So how I fixed this was this...and hopefully it works for you. I went back to my project, and basically started to delete effects, titles, and generators that were over and on clips towards the end of my timeline. I didn’t record my screen when this was happening, so I can’t show you exactly what it was, but I think what was causing this was a 3rd party title effect over my footage that basically had a bug in it and was causing this issue. I’m not sure why because I’ve used this effect before, but it was messing things up.
So if I were you, I would start deleting the effects you have near the end of your timeline, and see if that starts to make things run smoothly again. It worked for me so hopefully it works for you so you can continue editing in peace.