I recently discovered a fix for a problem I've had with a couple shows.
For some of my shows, new episodes--which are named correctly and listed as they are on tvdb.com--show up in Plex as simply "Episode X" (where "X" stands for whatever number episode it is). That is, there is no episode name or description.
I discovered that the episode will usually get recognized correctly if you: (1) remove the file from the directory, (2) refresh the library, (3) put the file back, and (4) refresh the library again.
Just thought I'd pass this on...