Final Cut extremely SLOW! Beachballing!

My Final Cut Pro generally has a small lag, but about 10% of the time, attempting the smallest task will cause it to freeze up and beachball for several minutes, making it impossible to work.

I edit on a MacBook Pro using an external hard drive (I've had the same problem on several different external drives) which has tons of free space. I store the raw video files and the FCP libraries etc all on that same drive. And creating a library on my internal hard drive and working from footage saved on the internal hard drive doesn't fix the problem either.

I work in proxy preferred.

The external drive is formatted APFS.

I regularly delete generated library files.

Not sure what else to try.

Any help is much appreciated!