Plex not showing movie images R9000 x10 or scanning media files for more than one library

I saw that someone previously had a similar, if not the same issue. Their write-up is as follows: "

Just setting up Plex on my R9000, connected USB 3 thumbdrive (32GB), and usin g my NAS as storage for my movies. But no image/poster is beeing downloaded, all movies are just grey boxes. Info and so on working fine, but only images not working.

Is there a solution for this, working fine when I used my NAS as mediaplayer."

In my issue, I have a server set up on my laptop that interfaces with my NAS just fine. However, my laptop is not ideal for streaming movies for several reasons (one being that my PS4 Pro and the router both use 5G and my laptop does not. But I digress) Anyway, I got the new firmware update that allows you to set up a Plex server on the router that uses an NAS. I purchased a 128G Samsung USB3.0 thumb drive, plugged it into the router and opened the Plex server. I added multiple directories into multiple libraries, but the server will only detect movies in one library. Also, in that library, media is matched and the info is working, but the artwork is not present (nor can I add artwork with the upload custom artwork function.)

This issue is marked solved on a previous thread, with the solution being listed as: "Solution is formatting to "OS X Extended (Journaled)", not working with FAT32 or EXFAT."

I have no idea what that means. Reformat the NAS? (I definitely won't be deleting 12tb of media for a reformat.) Or is it talking about reformatting the USB? If so, how would I go about that? I am very confused and frustrated with this whole process.