Removing inorganic materials and forgetting to remove the reactions for them in the entity file
Shouldn't make anything crash, a failed reaction just defaults to not being there.
Removing blood from vermin
Shouldn't be the problem, unless it is happening randomly, or they are trying to bring vermin blood in. Still shouldn't make it crash.
Creating plants and animals that don't exist in-game (either through the relevant token or by not giving the plants a biome) and then using their materials as reaction products and stockpile list placeholders (to fix potential variations on the thread stockpile bug)
I don't think that would do it either, might have to check with someone else though.
Removing all removable crafts
Nope.
Altering the skin material template to make it tan into the leather of one of the non-existent creatures mentioned above
Also no.
What does your error log say?
The snarkiness wasn't necessary, but thank you anyways.
It is required. Part of the contract.
Here's my 0.34.11 version, although I've been using the 0.31.21 version and I don't know if the same penning issue occurs in the latest version. The only difference is the Interacton (which instead is [FIREBREATH]) and of course the CREATURE_CLASS tag.
I will do tests on it in a second, though it will be for the latest version. Should be simple though. I am assuming it is the flyer or the amphibious tag, but science must be done to make sure.
***UPDATE***
Your lizards work fine, I can pen them with no problem. Might want to lower their speed, not sure why you have it so high.