Quest broke after entering a different place

The quest was entering this dungeon place (I don’t know the name, because it isn’t shown anymore and I play on german) and then search for the alchemy book. On my way to the marked spot, I sidetracked and found another dungeon entrance, which I investigated. The quest was still to enter the correct dungeon, but after a while it updated to searching for the book. Now I went to the marked spot and nothing happens here.

Sorry for not following the bug report format, but I didn’t know how to put this into the format.