There was some scaling going on with some of the footage, but I don't think that was the issue (I was putting 4k footage into a 1080p timeline at 50% scale).
Thanks to a private message from @Kevin-Monahan, the solution was to start a new project and import the entire broken project into the new one.
This worked for boith of the projects that were manifesting this issue, and I have not clue why, but I'm glad it is resolved.
The app has not been updated since then, and trashing preferences and any other solution didn't work either.
For future readers, all I did was:
1) Open a new project and save it in the same file location with the same name but add something like _B or _test at the end to distinguish the file.
2) go to your project panel, right click and and select "import..."
3) select the project that is giving you the issue, and click "Import"
4) select "Import Entire Project" and cllick "OK"
5) save the file
6) test to see if the problem was resolved, and if resolved, you can delete your old project file, and rename your new one