This problem is related to a known bug in the Android OS, you can read a little about it here.
What you can do is go to drupe settings, tap "Enable notifications". It'll probably show you that the drupe notifications are enabled, due to the bug. Toggle this off, reboot the device, and then go there again and toggle the setting on. This should solve the problem.
Sorry for the inconvenience, we're doing our best to fix this. Here's a puppy to compensate you!