XP is no longer generated when smelting armor or tools into gold or iron nuggets. This happened since updating to 1.17.10, but I do have the Caves and Cliffs Experimental Game Play enabled. The error occurs both with furnace and blast furnace, with and without hoppers. Although individual nuggets do not yield much XP, I am smelting enough at a time to have registered XP gains, and it is not being diverted to mending etc. Smelting of other items (i.e. raw copper into ingots, or cobblestone into stone) still gives XP. Smoker seems to work fine as well.

To reproduce...

1. Smelt 64 pieces of gold armor in furnace or blast furnace using a bucket of lava.
2. Remove fully smelted stack of gold nuggets.
3. Gain no XP