Vertex-themes have been unmaintained for quite a while now and even simple pull-request have been ignored by the developer.
I still think that it is a great theme and also we have already invested a lot of time and energy in our Maia variation.
So I did my best and started fixing issues and adopting open pull-requests on my fork and @Photon also jumped in to help find and patch some problems created by the latest gtk3 updates.
The Cinnamon theme was still a bigger headache with the introduction of vertical panels and other new features and properties. I have now managed to adopt elements from Arc and Mint-y themes and it seems I have managed to make everything work again.
I’ll upload new versions of both vertex-maia-themes and vertex-themes now. Please test and let me know if you find any issues…