I have noticed over the lase few days that quests have been vanishing from my log recently. They have been exclusively Prospector quests (Marleybone and MooShu confirmed) which eventually find there way back in my log after I log in and out a few times.
I've never heard anything like that. The only time that has ever happened to me is during some of the Holiday quests. After the holiday ends it takes away the quests. I think its maybe just a bug or glitch? At least they don't disappear forever. Hopefully Kingsisle will fix this matter if it happens to happen again.
