@peatrick, did you check for a bad title in the metadata (particularly the mp4, not sure if avi have it or not).
In Windows, this can be accomplished by navigating to the file in Windows Explorer, right click on the file and select Properties, then click the Details tab. Check what is in the Title attribute, if it’s something that doesn’t seem like it will fit the Plex naming then it will match incorrectly. Should be able to just blank it out, do the plex dance, and hopefully it will show up correctly.
The split is nice to have, but personally I like it when stuff matches properly so I don’t have to mess with it in the case that I have something go terribly wrong and need to rebuild.