Missing Plugin error on footage that shouldn't require plugin

I'm trying to import some 4k footage that I have on an external hard drive. I'm also holding the library on the external drive. I have it transcoding into optimized and proxy media, on previous attempts to import I've also skipped the transcoding and tried to work with only the original. As I type this, only Optimized media is giving a Missing Plugin error, though over the several times I've tried reimporting the footage the error has shown on proxy and original media as well.

Often the error appears after I've already used or looked through some of the footage without apparent issue.

Some troubleshooting steps I've taken:

host the library on the internal drive, unsuccessful (and impractical for workflow if it did work)

checked for latest MacOS update, updated, still getting errors

Changing the Quality preferences from "Better Quality" to "Better Performance" seemed to have an effect once, but I haven't been able to replicate.

Could this be some kind of issue where the external drive isn't fast enough? This is a fresh install of Final Cut on a brand new MacBook, did I miss a preference when I first set it up?