Not ringing for incoming calls (Micromax Canvas Tablet P480 - Android 5.0.1) I have Micromax Canvas tablet P480, using Android 5.0.1.

When screen is locked it does not ring for incoming calls. Why?
(But rings when the screen is unlocked)
Due to this I am missing many calls.
Anything I should change in the settings? or is it a bug?
I tried all the audio profile setting as well as notification setting, including interruptions for priority calls.

Please let me know if you need any other information.

Any suggestions will be greatly helpful.
Thanks!
Suggest you to set any of the screen lock(swipe, pin, etc). and try ringing, and then even when screen lock, phone rings. It worked for me.