Plugin breaks theme customization

Hi,

Great plugin, except that it breaks theme customization (Appearance -> Customize), at least for my installation. On the theme customization page, the menu in the left top corner loads, but then page load breaks. No theme preview, and hitting the menu buttons does nothing.

I do use multisite, but apart from that, I’ve tried to rule out any other culprits – deactivated all other plugins and tried different themes – the result was always the same.

Thanks!

https://wordpress.org/plugins/ultimate-fields/