VLF-ONE has always shipped with a set of themes for Windows desktop mode. That set has been expanded to include new themes for Material Design mode. This should cause no impact in an existing application unless you are using material design mode and have restricted access to the shipped themes and/or if you have created your own themes.
Technically, the #VF_SY170O theme object now has a property named ForMaterialDesign that defaults to False. If you start your application in Material Design mode, and no theme containing ForMaterialDesign=True is available, your application will fail. To resolve this, modify your theme setup logic to make sure that at least one ForMaterialDesign=True theme object is available.