Hi Stephen-
Jeff with Plugable Technologies here: I just wanted to suggest that the issue you're describing sounds like it could possibly be related to the USB3VGA not detecting the EDID from the projector.
A possible solution would be a shorter VGA cable to the projector. An active USB extension between the PC and the USB3-VGA instead of a long VGA cable to the projector would be the recommended setup here.
Please feel free to engage us at
http://support.plugable.com or via email to
support@plugable.com
I hope this is helpful!
Best wishes-
Jeff Everett
MCITP Enterprise Support Technician
Plugable Technologies