Panels in Premiere Pro 2018 12.1 unresponsive

This problem occurred for me the other day while I was editing. I have a project with around 40 video files and about 35 audio clips with several sequences. I was editing the first two sequences smoothly and without any issues, however upon starting to work on my third sequence, the panels suddenly became unresponsive. I am still able to playback and edit, but the panels only appear to visibly acknowledge an action once another action has taken place.

To give an example, if I highlight a video clip on the timeline, I can only see that I have highlighted the video clip when I press play (or take any other action). Then with a highlighted clip, if I click off it to un-select it, it stays frozen on the previous action until I press play/pause/whatever.

It's not a programme-killing bug, but it really slows down the edit process. I don't think it would be a hardware-related issue, as only a few days ago I was editing on this project file just fine. I've tested in other project files, and they seem to be working as they should.

Any idea what this could be? I may have to end up splitting everything into separate project files, but surely Premiere Pro should be able to handle that much data? I've worked on much bigger files, so I can't see what the issue would be.

Many thanks for any help or suggestions given.

(FYI, this problem occurred when I was working on this project in the 12.01 build, and the update to 12.1 didn't fix it)