Could it be usb bandwidth saturation (added other usb devices(webcam/printer, etc...) after driver install.
Yes, most likely it's a USB-VGA adapter
Tell me when will support Windows 10 1809
On the manufacturer's website - AMD Chipset Driver
(Note) Win10 ver.1709 \ ver.1803 supported. Version [10/18/20/02]
On AMD website - Revision Number 10/18/1810