Mod runs and loads fine and I can see/craft the recipes in JEI but they only mine 1 block rather than the 3x3x1 they are supposed to. I'm on Minecraft 1.14.4 and Forge build 28.1.0 (version 1.14.4-forge-28.1.0).

Updating Forge solves the problem. I only tried with 28.1.0 (where I can confirm the issue) but it works with the version I used for development (28.1.116). I don't know since which version the issue is solved but I recommend updating to 28.1.116