Upfront Builder active theme out of date / not updating, although it saves in Builder


I am updating my active Upfront Builder theme yet it is not updating when I view it logged out or when using Upfront.

I have exported the theme and uploaded it, without effect. I then deleted the theme and then uploaded it, also without effect. I have other sites on this server using Upfront Builder with the theme updating as I'd expect it to. I can continue to access the Upfront Builder theme, which looks as I'd expect it to, yet I also cannot save Font settings which reset every time I access it.