BUG! Secondary monitor video preview in Vegas Pro 14 b201 is broken if Windows 10 desktop UI scaling is set to anything other than 100% on the preview monitor.
Unfortunately in many cases it isn't reasonable to set scaling to 100%.
Many folks editing on a laptop use their desktop monitor as primary when "docked" and the laptop monitor as secondary. For high-end ultrabooks with 13" 4K displays, if you set the UI scaling to 100% the laptop is completely unusable as the Windows UI is too small to use.