I figured out what caused the problem:
A few days ago I did something I never do, move the entire AVCHD folder from my Canon onto my external, thinking that’s faster than importing all the media via FCPX.
Well, as soon as I removed the AVCHD folder from the external hard drive, BAM, my external hard drive showed up under my Events again in FCPX.
Don’t know why that was the problem, but problem FIXED.
Thank you very much for reading!