First time I've seen this. I've been using Offljan's Vertical Menu module quite a lot recently. Recently, on an older site I was updating, I added VM (had not previously been installed). Your CSP plugin was already installed from the sites inception.
I got an error in their module (in the beckend) and was sure it was their module's issue (I had no visible errors anywhere else). I turned on Debug in Joomla's Global Config, and it threw up this error:
Call to a member function isAdmin() on null
I know that Joomla 4 will have this functionality built in, but it's a few months away.
I am using the Twenty Twelve theme with a couple plugins and been trying to implement Content-Security-Policy headers but having a tough time. The only thing that worked so far was to allow everything but that defeats the purpose. I am using Chrome to read the errors but have yet to make it work.
Anyone making it work can provide an example of their configuration? I understand its not the same for everyone but just curious what a working configuration would even look like.