Could someone CAREFULLY EXPLAIN what causes this bug?
In the dead forest (east of the imp village) there are 2 of the ingredients required by the alchemist (Blue Larakiri root and Grey Quisirisi fruit). Before talking to the imp alchemist you can safely pick these up, but moving them in your inventory can or will (not sure if it is consistent) trigger a quest entry so that the game thinks you are further ahead than you are, and subsequently does not trigger a cut scene required to get the third ingredient.
This bug can be avoided by talking to the alchemist first when you enter the forest (a cave a bit south east of the entrance) or by not moving the ingredients in your inventory.
slant;
If you email support at larian.com they should be able to fix or bypass the entrance. There is plot related stuff in the cave so just adding the mushroom to your inventory would not work (or it might, but you would miss some stuff).
