I had a problem with page flicker using Pure & Simple; tried your suggestion of 3/31/19 and a number of other things and nothing works. I am now seeing the flicker on your demo sites as well, and I wonder if there is something in your theme codes that can take care of this issue. Multiple browsers, PCs and Macs both.
https://demo.styledthemes.com/?theme=Pure%20Simple
https://demo.styledthemes.com/?theme=Nora
and several others.
We have a reasonable fast internet connection but it may not be as fast as yours. Perhaps there is a test you can try to see what it looks like for other people.
You said:
The page is loading for me quite fast, hardly notice any kind of flicker. You can try to do some optimization on the site, first try to move the custom css from the customizer to your child theme css file in /wp-content/themes/puresimple-child/style.css
See if that helps.
You can also try to force the logo height to be fixed so the header have a preset height and it won’t be “moving the rest of the page down” until your logo image loads fully loads, try this CSS
@media (min-width:1024px){
.logo img {
height: 134px;
}
}
.
