It turned out to be "The Working Classes," for me and it seems multiple players have listed fixes for this in the comments on the mods.
One fix that you can find in the comments is to change a file to remove the erroneous behavior, the other that you can find there is to get AzureTai's fork of the mod that contains a fix. I recommend reading the comments yourself, before deciding.
One thing to note is that the first time that you look at an anvil after fixing it, the game will hang for a bit generating the help info, but start working again pretty quickly.
I hope this fix works for you, too!
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Pekkhum's post in Need help with Worldcrash was marked as the answer