So I gathered a lot of herbs in advance for my Healer's shop. After that I placed a new barn for a new settlement which was closer to the shop. Now my first barn is stocked on herbs, but my healer won't go gather them now that I have a second barn closer, which is empty of herbs.
This has to get fixed, as manually harvesting herbs for the second barn is just ridiculous.
TLDR: The "pathing" of the Healer has to be improved so he/she would gather herb's from any barn.