There is a pre-loader that is being applied to the site. You need to either delete the pre-loader or set it to display:none when the site is opened. In the attached screenshot I used browser dev tools to set the div with the pre-loader display to none.
If you want to disable or control the preloader in Webflow you can also do this by going to interactions and setting a page load animation. This Webflow University video may be helpful.
