So I'm trying to create a railgun spidertron and for some reason I can't. The assembler needs four regular spidertrons but it only allows me to insert up to 2. Also it did work once when I wasn't looking, so I'm even more confused.

Edit: So I did a little more digging and found it's just an issue that spidertrons don't stack unless they're identical. No equipment, no logistic requests, no pinned items, and even the "trash unrequested" setting separates them. I had to increase spidertron stack size to figure that one out.