When I recycle a Mk 3 spidertron from the the mod Actual Spidertron Tiers, the factory is only returning 1 Mk2 spidertron instead of the 3 that is in the recipe. Note that the factory is set to be 100% efficient.

I will not be surprised if the problem is in the spidertron mod...I've found a bug in it too

Ahhh, I looked into it, and this is actually an unfixable bug.

Spidertrons (the items) cannot be stacked, therefore the max amount of spidertrons (as ingredients) that can be returned from a recipe is 1. I don't believe this limitation can be modified, at least I haven't looked too closely into it, just enough to know that it doesn't work out of the box (causes an error on load when attempted)

I remember the last time this was reported was due to some power armor mod that required light and heavy armor, but another mod added equipment grids to them and made them unstackable. I believe the same would apply if any mod tried to use multiple vehicles as part of its recipe; it just doesn't happen very often

EDIT: I tried running the higher tier spidertrons through the recycler, and didn't get any output, which I believe means they forgot to add the recycling recipe as well (I wonder if the base recycler would be able to process this correctly)

No problem. I'll remember your answer for all the mods that have unstackable stuff. Thanks for looking into it.
Your mod, for me, is a "base mod" for all my plays. 8-)

Yup, I doubt you'll ever run into it again, since this situation definitely doesn't happen in vanilla/space age, and only very specific mods like that Spidertron mod ever use multiple unstackable ingredients in their recipes.

But also thanks! I'm glad to hear it, I feel the same way about this one, my very first release on mod portal lol