My iPod won't sync some albums

I have my music stored on an external harddrive. I had iTunes installed on computer A. I just bought computer B. I exported my library from A, got it working (mostly) with computer B running version 12 of iTunes on Windows 10. But.... When I check some albums, they won't sync to my iPod.

Some additional info:

I don't have enough room on my iPod to put everything on there, so I do NOT have "Entire music library" selected in the Music tab.

In the Summary tab, I have "Automatically sync when this iPod is connected" checked. I also have "Sync only checked songs and videos" checked.

I have verified that I have enough room to add the album in question (there are 8 that I'm trying to put onto the iPod, but I'd be happy if we could get the first one on there to start).

Thanks in advance for any pointers....