Telwath

Engari seems to be bugged. Whenever he asks me to talk to him, I cannot initiate a dialogue. Instead he immediately suggests that I should speak with Humaire. This occurs at each stage of the main questline. I have finished the DLC in the meantime. And now I have found out that Engari was supposed to send the Watcher on several artifact hunts. However I did not get any of those. Is the completion of those hunts required for the final upgrade of soulbound items like the Survivor's Tusks helmet?

Same here. My watcher sided with the Royal Deadfire Company and killed Queen Onekaza but not her brother. Scyorielaphas helped me fight the creature in the text sequence. On arrival in Ukaizo -> same issue as described above. (As a side note: In the text sequence, the RDC's submarine is always mentioned … even if I use my junk to cross Ondra's Mortar.)

I actually DO have the last ingredient in my inventory. Don't know, how and where I got it. I did not buy it from Jacob though.

I talked to Pietro at King's Coffin and was asked to "Speak to Rosenella" at the Radiant Court. However, when I talked to her, there was no dialogue option concerning the quest. While exploring Dunnage, I had found all of the ingredients which were required for the next stage of the quest - before talking to Rosenella. I could even return to Pietro, give him the ingredients and receive the gem. However the quest log would not mark the task as completed.