So my box is full with 6 seed types. It has Ranarr, Irit, Avantoe, Kwuarm, Toadflax, and Snapdragon in it.
I also have Cadantine, Lantadyme, Dwarf Weed, and Torstol stack in inventory.
The seeds I have noticed it fail to put into the box are Avantoe and Irit so far. But when I posted earlier and said it was working, I watched it click the Fill option on the Seed Box and put an Avantoe seed into the box. But around 2-3 hour mark, I noticed it stopped clicking on Fill and just left the seeds in the inventory.