This happened to me on the Flame but it can happen just as easily on Flatfish. The thing is that if any of the core apps has its database corrupted somehow you’re left with a useless app and no way to recover besides a hard reset of the whole device.
With me there was some issue importing Facebook contacts that messes the Contacts database. The contact list became unresponsive for all contacts that were from FB or had a profile linked. Without being able to go into the contact view for those contacts there was no way to remove them and I was left with a contacts app that didn’t work and no way to empty it besides a “reset from factory” on the device.
I think that all core apps or even the system should offer us the ability to empty the indexedDB storage for the selected app. This could go into settings -> storage. We could have all apps that have indexedDB records listed there with options for erasing the whole storage.
Without this there is no way to recover from some faulty import operation. This can also happen to Email and Calendar.