Slight menu lag when using Vulkan on Linux

When using the UE4 Editor with Vulkan there is a slight lag when navigating through the menu options. This lag is not present when launching with OpenGL nor is it present on Windows with -vulkan. 

This was reported and tested in 4.21.1 (CL-4613538). This was reproduced in 4.20.3 (CL-4369336) and Main 4.22 (CL-4647769)

1. Launch the UE4 Editor with -vulkan and open any project
2. Click on File or Window and move the mouse though the options

Results: There is a slight lag when moving the mouse through the menu options

Expected: No lag when navigating the menus