Hi there,
sorry for the delay, I am using a theme builder (pro by theme.co)
I sent a ticket in to those guys as well and they have responded with;
‘you need to reach out to the developer of the downloads manager plugin and mention that the menu is changing or overriding the menu on the downloads page.‘
This site is several years old, and worked ok originally, at some point the menu has broken but just when you click a category.
Any help would be appreciated.
Thanks
Tony