Whenever I try to brew anything use grass (absinthe in particular) the cauldron will not take the grass. Is this a bug or was the recipe removed?

I am having this same issues.

The recipe has not changed, somehow grass must fail to recognize for you.
What Server software are you using? Do /ver

Clean install, still isn't working. The grass isn't even recognized as an ingredient. No error messages. Java 8. Everything else in the plugin works perfectly.

It tried to add the off hand to the cauldron, it is fixed in the newest commit. See here #130