I though the same and quried it with them and this was their response:
It seems that we are seeing duplicate element IDs due to the mobile navigation menu having the same IDs as the regular menu. The reason that you are not seeing this in the static showing of the HTML source code is because our Accessibility checker looks as the dynamic content of the page where it also finds the mobile menu.
So I would argue that the platform is right in showing these as issues, because the element IDs actually appear twice/is duplicated.
To resolve these issues, I see two ways of going about it:
One would be for us to cut out the mobile menu from the crawl, so we are certain to only see the navigation menu once.
The other would be for you to give the mobile navigation menu unique IDs that only belongs to the mobile menu, making all IDs on the pages still be unique.
Do you think it’ll just be easier to get them to remove thew mobile menu from the scan?