Hardened end stone uses 4 end stone in a 2x2 pattern which conflicts with vanilla MC's end stone bricks recipe. It's probably a bad practice to overwrite default MC recipes without a good reason.

There are two logical resolutions to this:

1. Change the recipe. (For my server I updated it to 9 end stone)
2. Require a mod like polymorph as a dependency which can handle conflicting recipes. This is IMO sloppy and a bad solution, but would work.

@Craftjakob Thanks for the quick response. I manually edited the recipe inside the jar file so I'm fine for now, I just wanted you to be aware so you could update it, appreciate it!
I assume you fixed the recipe, what was the end result? 9 end stone > 1 hardened end stone?

I have actually changed it to 8 end stone, because maybe someone have a mod installed, that adds compressed end stone.

Like that:
EEE
E E = 1 Hardened End stone
EEE

Or do you want more than one or another crafting recipe?

I had uploaded a fixed version for 1.20x

Or do you want a version for 1.19x?

I don't have a strong opinion. The solution that made sense to me was 9, and in the vein of compressed (without being actually "compressed end stone") I added a de-crafting recipe that reverses the 1=>9.

In hind sight, a lot of the older mods used obsidian (powder?) for hardened items, so maybe 8 end stone and 1 obsidian would make more sense?

But again, no strong opinions, do what makes most sense for you! Thanks!