I don't have any simple solution, seems like a combined hardware/driver problem, of course related to VNL in a sense, but nothing I have seen before. You can email support@quantumwise.com and provide more details, like the specific driver version and what's written in the About box in VNL, then we may be able to provide further hints. We have seen some other issues with 4k displays, they are not yet standard enough to necessarily support all applications 100%, although it's interesting that 13.8 works. Notably, in those older versions we didn't use shader technology which is needed for good performance once we get to 100,000 atoms or so. So one thing you can try is to turn shaders off, in File>Preferences under Graphics. It lowers the graphical performance, and some advanced graphical features in VNL are only available with shaders turned on, but maybe the bonds come back
