It is the camera. This is a known problem with the USB2.0 version of the ASI120 (the USB3.0 version works fine). Just google "ASI120 split frames" if you want to read more.
The issue happens mainly in conjunction with Windows 10 and then not on all computers. That's why the camera works for some people but not everybody.
In PHD2 you can try using the Directshow or ASCOM drivers, this has solved the problem for some but not everybody.
I had the same issues and eventually got a new guidecam. The ASI120MC is now being used for planetary.
The sad thing is that the camera is still for sale although the problem has been know for years