Following your advice here is a new ticket:
We want to show a mobile menu in off-canvas but there is only a grey overlay without content. What we did: We’ve created a mobile menu and choose it to be displayed as off-canvas. The off-canvas is checked as exclusively mobile. In customizer things look fine but it does not appear on iPhone.
I am going to try to turn off other plug-ins and let you know. Until than you don’t need to get active. Thank you in advance.