I had the same issue. In my case, it was a conflict with between Realtek Audio Driver and Nvidia. I uninstalled Realtek driver and control panel. Problem is gone.
Among the Services running on Windows you stop and disable NahimicService ... Or you uninstall the not very useful applications that use it to improve the sound effects of games, such as Alienware Command Center or Sonic Suite. This service interferes with the graphics card that Vegas uses for the UI.I had the same problem.
Thank you Etc. for pointing this out. I've just disabled Nahimic and will see how it goes.
Just stopping Nahimic in Task Manager/Services is not enough as it starts running again on rebooting the computer. To properly disable Nahimic, R click NahimicService in Services and then select Open Services. A new window opens. R click Nahimic service and click on Properties in the window that opens. In the context box that then opens, select Disabled in the Startup type field, then hit the Stop button and click Apply and OK. All done. Nahimic now remains disabled on rebooting the computer.
Besides of Realtek HD audio driver, I got this issue on Sonic application ("Sonic Radar 3" and "Sonic Studio 3") on my ASUS ROG. After uninstalling it, problems gone.
There is actually a way to make VP18 and NahimicService coexist, but this I can only say for a Dell computer with Alienware Command Center installed. In the path C:\ProgramData\A-Volute\DellInc.AlienwareSoundCenter\Modules\ScheduledModules\Configurator there is the BlackApps.dat file which contains a predefined list of applications that Nahimic should not affect. So I add the executable name vegas180.exe to the list and VP18 works. Unfortunately this solution does not work with Vegas Capture (which is a separate executable). In this case NahimicService must always be stopped.