I still have this problem with the battlez quests on ver 6.9.1. I'll start up the game, see the two battlez quests (none of the quests will be marked new) and then I'll play a free battle, usually win it, and then go back to claim my quest reward.
But when I do, those two quests will be missing, or all of them wil wi missing. Immediately after exiting the travel log, the two or four quests will appear marked new. This phenomenon can happen multiple times a day. I can't get any mints to save up for the contain-mint this way. I must have missed out on about 10 mints by now.