It would be hard to say. You need to find where the menu is show n the page and then you need to follow the code through. More than likely I’d guess that there is a filter somewhere that is applying the changes to the menu, however, there are a lot of possible filter hooks and methods that this could be done. So basically find the function that’s showing the menu, look at that function, look for any apply_filters() calls and then search the theme for filters that may be running, continue following the code and looking at filters until you find it. Welcome to debugging.
