Cannot customize menu appearance from Upfront Builder


I’m using Upfront Issue theme.

Whenever I try to custom the appearance of my top bar menu, via Upfront Builder, clicking on the menu, then cog icon, then Appearance section, it always revert back to default.

If I add a new Preset appearance, it is applied and it seems fine, but when I click on SAVE THEME, although I see it correctly in Upfront Builder, it is not displayed correctly (that is with my customized style) live on my site.

Refreshing Upfront Builder, I see the menu indeed back with the old style.

Same thing happens if I edit the DEFAULT NAVIGATION appearance, or any other appearance style.

Please help, thanks!

Site is still offline, cannot grant you support access yet.