As far as I know this can be a sign of a few things:
- There was an error when you downloaded the APK, and so you need to re-download it.
- There was an error duing the install of DD, so you need to re-install it.
- Your phone is too old (whether that be the hardware or the operating system version).
- Some other compatibility issue with your phone.
First things first, always restart your phone just to make sure that doesn't fix it. After that you can try point 1 and 2. If the issue is caused by 3 or 4, I'm afraid I can't help there. There may be something else causing the issue as well, but it's near impossible to fix something when you don't know the cause.
To my knowledge, they're in localStorage. The issue with that is, your phone needs to be rooted to access that. Anyone rooting their phone claims full responsibility for doing so, I do not encourage nor endorse doing that.