Two days in a row i’ve used my silver key for the harp mission, both times when i fought the side monsters in the dungeon the game freezes after i finish killing them and i have to restart. lost 50 tickets and 2 silver keys 
also i am using a galaxy s6 and this is the only instance in the game that seems to be bugged for me
Time to change to apple iphone…
Not sure if Dev’s took action to fix it but i tried again today and it worked fine no problems!