After closing the off canvas menu either with the escape key or pressing enter on the close button, the off canvas menu items retain focus; after tabbing through the menu items, the page loses focus, such that the tab key highlights browser controls instead of links on the page. The expected behavior is for the menu toggle to receive focus when the menu is closed. This can be experienced with any GP site, such as https://gpsites.co/split/
I’m not using Split. In the Private Information section, I included a link to the staging site where it is not working. Included again herewith. It is using the Off Canvas Panel option in GP Customizer settings. I have disabled all custom JS and CSS.
Can you try re-installing the theme and GP Premium?
And i am going to ask Tom to take a look at this topic, as i cannot see the difference between your sites and all the others i have tested which are working as i believe they should.