Premiere lags HEAVILY when I navigate to new points in the timeline, scrubbing is completely useless.

This problem is so bizarre that I struggle to put into words how it even manifests. I open my project and premiere initially renders whatever frame was there when I closed the project, if I try to move the playhead to another place on the timeline, it will lag anywhere from six to twenty seconds before rendering the frame. It plays everything back no problem, but takes absolutely forever to start playback. The other issue that is even weirder is that when I hit play, it often takes forever to actually start playback. I find that if I hit the spacebar four times it seems to snap the program out of whatever bug it's in, but that fix isn't very consistent or reassuring. In general, everything is slower and usually simple tasks like sliding a clip over and extending it will often times cause the rainbow wheel of death to appear if that aforementioned task is done too quickly, BUT the program never crashes when this happens, it just spins the wheel for five minutes (sometimes more) then will show the changes I tried to make in the blink of an eye and be ready to go again. The strangest thing is that if I open another project, I don't have this problem, it's just on two of my active projects.

I've updated everything and am running Mojave OS on an iMac Pro 3Ghz intel Xeon W, 64GB DDR4 RAM, and Radeon Pro Vega 64 16368 graphics card. Editing off of a Pegasus R4 with USB-C.