I noticed that using the logo on the main menu bar (I used it under the header) has the effect to leave blank the page into customizer, if you try to change the theme.
I suppose there is some conflict with the customizer.
1. Set navigation position to “Below Header”.
2. Upload Navigation Logo in “Customize > Layout > Primary Navigation”.
3. Change themes and try to enter the Customizer.
Is that generally it?
GP Premium requires GeneratePress (theme) to be activated, so if you’re changing the theme, you’ll want to deactivate GP Premium as well.