Custom menu choise not working

Can you replicate the problem using the default Twenty Fourteen theme with all lugins deactivated?

I can with this current theme and all plugins disabled

So it would seem that the issue is related to a plugin, yes? If so, If this works, re-activate the plugins one by one until you find the problematic plugin(s).

I can replicate the problem with all plugins disabled, doesn’t that mean it’s not the plugins?

Sorry – I misunderstood you. Leaving all plugins inactive, what happens if you switch to the default 2014 theme?

That won’t mess anything up permanently yeah?

No. Your theme & plugin settings are saved in your database and should be retained for future use.

It allowed me to change the menu with the 2014 theme

In that case, you seem to have a theme problem. What theme are you using? Where did you download it from?

FlexFit: https://themeforest.net/item/flexfit-responsive-business-wordpress-theme/2630250

It’s kind of weird in that when I try to change the menu it’s labeled as “Custom” when in other themes its like “Main menu” or “top menu”

Your theme supports 1 menu. Select which menu you would like to use. You can edit your menu content on the Menus screen in the Appearance section.
Custom Menu

I’m sorry but as you are using a commercial theme, you need to seek further support from the theme’s developer/vendor. We do not support commercial products here.
Try https://themeforest.net/user/minti

Is there some place in the PHP I might find the antidote?