Unable to view navigation menu on Category pages

Hello,

I am using a theme called Foodpress.
I set up a menu set up in WordPress menu admin section as the primary menu for that theme. It works well on the home page and also on single post pages but not for category pages. It doesnt appear at all.

I am not a seasoned WP admin but I am aware of the normal php files used within themes. I have done some research into this but have been unable to find the root cause of the problem. Unfortunately there is no tech support available for this theme for some reason.

I have had to switch off the primary menu until I can find a solution.
Some advice on this would be very welcome