In order to make display items restock, I turned them all into containers that hold the actual item. These scripted containers are supposed to disappear when the item is sold and reappear when the item is restocked via script. However, this means there's probably over 100 containers in the cell.
I checked, their ownership is set to the right merchant npc. I think the game just can't handle that many containers belonging to him. There's over 200 items that he's supposed to be able to sell, and he only sells about 100 of them. The rest all stubbornly sit in their display containers being unsellable.
It seems like he won't sell anything from the scripted containers, just the unscripted containers. I have never had this problem with scripted merchant containers before, so I think it's just picking the unscripted containers first and saying, "You want me to load ALL these other scripted containers too? Screw that!"
THIS svckS.
What can I do about this?