my fps vanishes when i tap on my mobile screen

i didn't wrote any code for any actions when i tap. i have used unity cardboard to make a virtual reality game. i have generated the apk and installed in my mobile. though i didn't write any code or didn't set anything for tapping, if i tap my fps vanishes automatically. i am a beginner. how to fix this error.

N.B: Under First Person Character I have added Cardboard Main. Under Cardboard Main's Head, I have added the arm (3D Mode).