They are certainly same copies of the maps. The pc's in question are two in my house, and one at my uncle's house, all of which I administer.
I'm going to try reinstalling everything from scratch. I have installed mods, patches and I believe I have done the same procedure on each but... not 100% sure... After that I'll report back.
Edit: Are all related game files located in the RA2 folder? I mean, does RA2 cache or store temp files anywhere else like %tmp% ?
Edit2: Reinstalled, applied patches, installed new maps, everything works as expected. I have no idea what was causing the issue though.
Edit3: Check this out ->
1. start YR, Network, New, pick a custom map
2. have another user join who also has the same map
3. exit YR, open said map in text editor and under [basic] section, change Name= to a different map name, or in FA2 save as a different map name
4. save as a different file name than original
5. make same changes to other user's map file
6. start YR again and try to load any custom map
7. when other user tries to join, it says (for me) that that user does not have the unofficial map and same thing when that user picks a custom when I try to join their game
My best guess is that YR is caching the map file names with the hash or something like that and not updating with the new file name.
Edit4: FA2 does NOT update the [Digest] by simply saving the map. I had to open the .yrm in notepad, remove the [Digest] section, then open the map in FA2 and save it to update the digest which solved all my issues