Some slow motion clips are choppy, others work.

I often run into problems with my slow motion clips coming out choppy. The sequence is set to 30 fps and my clips are in 60 brought down to 50%. Of all the times I have run into this issue I solve it by either nesting the clip in another sequence or optimizing premiere to use more memory but this happened out of nowhere. I was in the middle of editing and every slow motion clip was working fine then all the sudden while navigating my timeline 3 clips just went choppy as you can see in the video provided. One clip whether nested or not will be choppy then the following is completely fine. I am at a loss for how to fix this if anyone can help it would save me big time, thank you. I have the premiere view where the 3rd, 6th, and 7th clips are choppy but in the other exported video provided only clip 6 is choppy. Again all of these clips were working fine before. I can only think I somehow mispressed a button and this happened with no warning, but why would premiere have a chopping hotkey.