The Expedition Quest Chain.

Hello, dear GGG team, I have a question: why does it say “4 out of 5” on the right side even though I've killed all the bosses and completed the entire act chain? There are no more quests left. Also, regarding the lockbooks, I don't understand where or how they drop. I’ve attached a screenshot below showing that I have no quests left and that it’s a bug—or maybe someone knows—that it says 4 out of 5 bosses. I’m waiting for your prompt reply because I don’t understand what the problem is.