Error while loading recipe prototype "unstable-bp-buried-biter-nest" (recipe): Key "icon" not found in property tree at ROOT.recipe.unstable-bp-buried-biter-nest.icons[1]
Modifications: Alchemical Ore Conversion › Bob's Functions Library mod

I use all bob's mods and I guess it's related to Bob's Metals, Chemicals and Intermediates mod

This likely has something to do with how I auto-generate recipes for resources. It's catching something that's not a resource and trying to generate recipes for it. My Lua code for that is... a bit of a mess. I'll see what I can do, but my Lua programming skills are not the best.

I think it may be an icon generation problem when the source icon is composed

I think it may be an icon generation problem when the source icon is composed

Very likely, yes. It's been a while since I made this, but I do generate icons dynamically for all the ore conversion recipes. Seems like I'm trying to pull an icon variable whereas whatever this object is only has an array of icons. The bigger question is why the mod is even trying to generate ore conversion recipes for... a biter nest object?

My logic for determining what is and isn't a resource is a bit roundabout, because Factorio has so many different ways to define those. I think the issue might be that I check for several excluding characteristics and let it through if it matches none of them. Could be Bob's biter nest thing doesn't match any of them, but still clearly isn't a resource. Do you happen to know which specific Bob's mod that's from? Or is it literally in the Library mod?

The "bp" reminds me of "Bob's Metals, Chemicals and Intermediates" which has the technical name bobplates (https://mods.factorio.com/mod/bobplates) but the biter nests are more related to "Bob's Enemies" (https://mods.factorio.com/mod/bobenemies), so it is possible that it is the use of the 2 at the same time, which could explain that it is bob's library that reacts that it must do at least a large part of the link

If you add to your exclusion conditions the fact of not having an icon, this should solve this problem