I'm wondering if anyone's found a solution to this yet. Like the OP, I'm in the endgame, working on getting the last medals. I got the first herbal one making healing potions with a sage in one of the early towns, but I don't get credit for making potions with Kai in Patrick's Tower. Tried saving/checking stats a few times, then quitting and going back in. The odd thing is that the herbs show no decrease in number, unless I give them to another character, at which point the decrease registers - but no potions.
I thought it might be that the character with the herbs has no inventory space, but it didn't even add potions to the ones he was also carrying (graymold salve, energy elixir).
I don't usually care about the medals, but I have so many herbs I'd like to finish this one off.