I took a few others as well, here:
4 years ago(+1)
This bush in particular was completely unresponsive, just making the overlay disappear for a moment:
Thank you for detailed screenshots! I managed to find the problem and it is now fixed, I have updated the game files in case you wish to re-download them with the fix. It is possible that some of the plants that generated prior to the update might still give Peppercorn, but once you cut them down and new ones spawn they should spawn the correct plants now.
On a side note, finding Lemon and Grape seeds in the forest plants is okay, I just didn't word that correctly, what I changed was that you couldn't get them from the actual Grape and Lemon plants when harvesting them on your farm.