Often, after closing vantage, it locks up the UI of the render dialog and everything becomes greyed out. Especially after livelinking, and from withing vantage rendering highres still
Only way to recover is to switch to different renderer and then back to vray gpu
Are you closing Vantage while in Live link or you first close the live link via the button in the toolbar and then Vantage? If you only close the Vantage window, the live link session would still be running from Max’s point of view and would resume rendering as soon as you start Vantage again. That may be the cause why the render window in Max is locked.