Some files won't load into viewer

So, I’m relatively new to this, but understand how most of it works. I’ve had no issues adding any files whatsoever, so far, but I recently ran into a problem where a couple seasons of shows I have won’t show up. They are .mkv and .mp4 files, and to my knowledge they both h264. Both are 1080p quality and play no problem in vlc or whatever. It’s just like Plex is choosing not to recognize them for some reason. Any insight would be appreciated.

Which OS are you using?

You didn’t say and you ended up in the Linux section.
Given your lack of details, I suspect you might be using Windows?

Apologies.

My media server is hosted on a seedbox that runs ubuntu 20.04. I’m not entirely sure what details I should be providing, to be honest. I manage the seedbox on my laptop, where I test to see if the files loaded into Plex. When everything is good to go, I only really use one TV to watch anything.