In the last couple updates, upon trying to join a world I've been hit with a notification that my datapacks are invalid. I've checked by disabling only this mod and the issue has gone away, so it's definitely something to do with reworked metals

Which Minecraft version are you using? 1.16.5 or 1.17.1?

Found the problem. It was due to copper blocks being referenced as minecraft:copper_block and minecraft:raw_copper_block as in 1.17 instead of reworkedmetals:copper_block and reworkedmetals:raw_copper_block.

Fixed in version 1.1.2

Apologies, I didn’t even know there was a 1.17 version otherwise I would’ve specified, I’m using 1.16.5

I was getting the same problem.
In addition to that, in the prior version ReworkedMetals made a lot of modded & vanilla cooking recipes uncookable in vanilla & modded furnaces/forges/ovens.
MC: 1.16.5
JDK: 16.0.2
Forge 36.2.5