like every two or three days
This means that you are using a particular workflow that enables this bug or you have a faulty device. It would be nice to have it so we can easily reproduce it.
There is this thread: [4.0.1.48][4.1.0.23][4.4.0.64][4.5.0.16][5.0.0.29] No notification sounds (ringing, SMS, alarm) and I’m pretty sure it’s the same bug as defined here. Please, continue there.