for me it is only rotating on yaw and it is facing backwards. I noticed only if I move my mouse in a very tiny area around the absolute center of the eye does it face forward , and maybe also get a slight bit of pitch. Otherwise vertical mouse movements dont affect pitch, only yaw. Im using chrome Version 74.0.3729.169 (Official Build) (64-bit) Tested in firefox and same issue.
Perhaps looking at my utility example may show something more , i know it is not your raw api code , but this was a fully working example for many months already. which now does not work correctly :
It used to move and look at the selected object from the selected direction with a small offset added. Now it seems to go to very bizarre positions. The direction is correct. but the position of the camera is messed up. I have not worked on anything relating to this , but I will check to see if maybe I broke something.
For your own api example I can make a video for you if you like