Why is my site loading so weirdly?

Here's the site - http://barberacademyoftexarkana.com/

It's still pretty basic, just three pages. I'd like to move past the design issues.

I created it with Upfront Builder. On every browser I've tried, it loads with one text style, then changes to a different style. At times, the menu loads noticeably slower than everything else.

This isn't the first Upfront site I've had this issue with. On this one, I have Performance-improving Behavior Changes set to Agressive.

What am I doing wrong?