Flash of Unstyled Content when I use Litespeed Gust mode optimization

When I enable LiteSpeed Guest Mode optimization, the website performs very well, but there’s an issue: on both mobile and desktop, the first visit to the site initially loads an unstyled hamburger menu before the page switches to its normal styled layout.
Let me share the screen shoot for you.
But after I turn off this mode, my Google PageSpeed score drops drastically. I admit this mode does make the website much faster, but I can’t fix the abnormal loading issue where the hamburger menu appears without styles at first. Could you please help me?

Start by reproducing the first-visit behavior shown in the attached screenshots with LiteSpeed Guest Mode optimization enabled on both mobile and desktop. Compare the initial hamburger menu with the normal styled layout and identify the cause of the unstyled flash; done means the first visit renders the styled menu while Guest Mode remains enabled.

Written by the indexing model from the issue text.