Series art - not there, no background.

So, after some time playing around in the Plex garden, I've come back to Kodi. I've installed without any serious issues, but I've hit a surprisingly irritating snag. 

I'm running on an Nvidia Shield TV 2017, and my files are shared from an NFS store off an UnRAID server. 

Anyway, I'm mostly working just fine. However, I have some series that won't show images for the series, whether we're talking on the TV or in a web browser. 

For example: 



But it's not a scraping error, because Agent Carter is the correct show. Kodi is pulling all the metadata about it. 

It's even pulling season art:  



I'd say this is happening with about 20% of my shows, and I don't get it. 

If I try to manually fix one (which is never the ideal option...) I get this:



...and that "Searching for more images" swirly will spin forever, as near as I can tell. 

As part of trying to work this out along with a freezing error I've been having I've gone ahead and wiped Kodi. There are zero add-ons running right now. I don't even have a movies folder setup, just this TV Shows. 

Can anyone make a suggestion here?