mobile navigation

Hello!

I'm crowdsourcing a question from a colleague: Do any accessibility pros have opinions on the use and accessibility of sticky menus, particularly with regard to mobile? Any good articles or opinion pieces I can send this person?

Thanks!

---Jess

If anyone can help with the following it would be greatly appreciated as I'm quickly becoming grey haired over it.

Basically I have a site that's navigation works perfectly on all local versions but has issues when testing the live site on the most of the same browsers (please note all files are identical in terms of those on local and live server).