Butter clarifying mixing mistake

The reason is that butter can inhibit gluten formation. It 'coats' the proteins that would form gluten. You knead the dough first to get gluten, and then add the butter afterward around the already formed gluten.

You can add it earlier, you just end up with less gluten and a more tender dough.

Creaming isn't usually done with bread, as its purpose is air bubble formation.

I can only guess that something from the herbs has "disturbed the balance of the mix" and is preventing it from setting.

Putting my chemist's hat on, the problem is similar to what happens when a solid reaction product forms an emulsion and refuses to precipitate. When that happens, there are ways to induce precipitation, but not all of them can be applied to food.

Try adding a pinch of salt - mix, and wait.

If that fails, smear a knife blade with some fresh butter and stir the mix with it.

If that fails, try cooling it.

If that fails, try mixing in a pinch of bicarbonate of soda.

There are other suggestions, but I assume you want to eat the butter once it solidifies. Ideally, you want to find that happening after one suggestion has worked. If it takes a succession of suggestions to find a way to solidify it, this is about as far as you can go without the product starting to "lose its intention".