I created a VirtualBox (Version 5.2.4) CentOS 6.9 x64 guest machine, and replicated it to have three identical machines with a base configuration. All three machines (being identical) resize dynamically and function as desired - automatically updating resolutions on window size changes.
The problem is that on one machine, I installed TigerVNC Server. (I needed TigerVNC specifically.) After this, it appears to have broken the resizing on this VM. It doesn't resize anymore to fill the VirtualBox window, and often has white bars at the top and bottom to fill the rest of the usable space.
How can I troubleshoot or fix this? It's rather unfortunate having one VM size differently than the others, and cumbersome to navigate a desktop with scrollbars. I believe the installation of TigerVNC Server to be the culprit, but have minimal VNC experience.