ZTE nubia n1- My screen completely locks down while playing audio

I have a ZTE Nubia n1 phone.

My phone completely locks down when I play audio from my Whatsapp chats. Power/ volume / fingerprint sensor/ touch nothing works just goes dark till the audio ends. Very rarely long press of power button works. Highly irritating.

Not even able to stop the audio.

Works fine if played from files folder.

Please help