Versions

Forge Version: 31.2.0
Mod Version: 1.15.2-4.0.21

Other Mods

https://gist.github.com/Lanse505/e9e473d1161dd998bec0ac1135ccb171

Logs (if applicable)

https://gist.github.com/Lanse505/0cbcfe3dc6b55518b4c86a8d6681de22#file-logs-L2285

There are a few of these errors spread through-out the log.

My assumption would be that you're not registering your recipe serializers to the registry?
Though I haven't had time to dig into your code to debug yet since I'm in Finals Week.

I'm not adding any custom recipe serializers, these are normal smelting / blasting JSON recipes using all vanilla functionality, but the issue may be that you've disabled ingots and so it's complaining as the ingots aren't available to complete the recipe? I thought I had implemented exists tags for the recipes but maybe not.

This should've been fixed long ago when I removed a few settings and fixed a handful of Datapack things that changed with 1.16. If you're still having issues let me know.