Hello,
I noticed that since the last patch there is somehow problem with the flasks.
If I use one, this no longer holds 30 minutes, I change the city or the dungeon, this is suddenly gone and the buff thus also disappeared.
What is that all of a sudden.
Are you sure you didnt log out?
100% just starting playing 
activated a flask 9:30 done a dungeon, moved to another dungeon and at 9:45 the icon disapeared on my buff-task…
if thats true, please log a bug report. I dont have that issue so I cant concur.
I give another try and then report but i remarked that yesterday already.