picture of myself changes to pixilated suddenly 4-5x per meeting

i thought my camera had gone bad. replaced it and same thing happens:

mid-meeting, randomly, the picture (of myself only) changes from normal to pixilated and wider angle. 

if i 'switch camera" back to built in camera and back again to external camera, the picture corrects.

then , randomly, the same error happens suddenly. usually 4-5 x/ hr.

help please