Customizer loads forever

Hey there,

absolutely beautiful theme, I am testing the free version right now before I purchase the pro version.

I have an issue in wordpress 4.9:
I just set up a site, installed the theme and the Mesmerize Companion plugin.
However, after installing the plugin and trying to make changes via the customizer, it loads forever when pressing the “publish” button. The changes aren’t made no matter how long I wait.

I’m running the latest wordpress, have around 5 other wp-sites running well on my host and as I said I haven’t done anything else to the site yet.

Thanks for the hard work!