I can't help you with ISO files, as I don't use any. So, I'm only guessing here, but...
When you open an ISO, MC (and the OS) treats this identically to opening an actual optical disc in a disc drive. When you play a "real" DVD or BluRay, they typically don't "end" when you finish playing the movie, they return back to the main menu of the disc. So, how this behaves almost certainly depends on how the ISO file was authored: whether it is set to auto-end, pause at the end, loop playback, or whatever choice was made when the disc/ISO was
created (in the authoring application).
I don't know how you made those ISO files, but therein might lie the rub. However, this sounds like it
could also be the issue:
There have been some reports of videos not stopping when they get to the end, and just sitting there at the last frame. Could this be what you are seeing?
If you are ripping individual episodes to ISO, then you almost certainly should not be doing this. Instead use
MakeMKV (or an application like it, but I'd strongly recommend using it) to rip them to standard media files. MakeMKV, unlike some other similar tools,
does not re-encode the video in any way and does not alter the quality of the video in any way. It simply converts the "formatting" of the video from the IFO/VOB format used by a DVD player to the file-based format preferred by computers (MKV in this instance).
This also has the benefit that the rips are quick, because it isn't messing with the video in any way, just copying the existing streams onto your hard drive. This is identical, conceptually, to ripping an audio CD to WAV. It changes nothing, just puts it in a MKV "wrapper".
It is a fantastic tool, and you'll probably be much happier with your Library setup if you go with this system of storage. For movies, if you want to preserve the menu system on the disc, then you might want to rip those to ISO, but otherwise, going to files is almost always the way to go.
Oh, and MakeMKV can convert the ISOs you already have (it can rip from those just like it can from actual optical discs).