Hiya, for example I am holding the skeleton data model, when I kill skeletons with it in my inventory or in the offhand it doesn't progress at all. I heard that you have to get the last hit with the data model and I tried that but nothing seems to work.

Are there any known incompatibilities? Everything in question appears to be vanilla from JEI. Have tried with skeletons from a skeleton spawner in survival and creative.

Any help is massively appreciated as I'm looking to throw this in a modpack as a part of progression.

The data model has to be inside a deep learner to gain progress from kills. That deep learner has to be inside your inventory, and the deep learner hud only shows if the DL is in your hand.