I reinstalled Vegas V 387. Reinstalled Vegasaur and Vasst. The icons were always seen when I customized the toolbar in Vegas.
As of yesterday with my HP Pavilion 32QHD monitor the icons appeared fine.
Today ( 2-13-20 ) I purchased a Samsung 4K monitor started up Vegas and did not see the icons. I reinstalled all programs. As you can see the icons are available but not visible until I put my mouse curser over them.
I am running a Radeon Vll latest AMD drivers. Just like I was yesterday. Same DP cable as yesterday. The only change is the monitor.