Navigation become bigger for a second

Yes it was unchecked. Should it be unchecked? What is the default setting for this?

I wonder, because they mentioned, that my site use Generate Press option for this. How can that be, if this is unchecked?

Just checked with Tom and there isn't a way to turn off generate-style-inline-css without losing all of the customizer option output.

Have you tried turning off Optimize CSS Delivery as WP Rockets suggested?

Yes in wp-rocket it was turned off. I have turned it on with no effect. So I have tuned it off again.

But what about the GP Setting? Should it be unchecked or checked? What is the default setting for this?

The default setting is unchecked.

You can see the explanation here:
https://docs.generatepress.com/article/cache-dynamic-css/

So should I check this? Or what did you recommend?

I would say so yes :)

I have checked this now, But the same problems. But it seems, that in chrome it is a bit better (at least forthe moment), but not in firefox.

That option definitely isn't for solving "Flash Of Unstyled Content".

So have you tried turning off Optimize CSS Delivery as WP Rocket suggested?

Yes, I mentioned that in #927302

I assume the issue disappear if you simply turn off WP Rockets?

If that's the case you will need to check with their support some more.

I have not tried to deactivate wp-rocket. Because I have many sites with GP and wp-rocket and I never had this problem.

Because I have many sites with GP and wp-rocket and I never had this problem.

So isn't that basically suggesting neither GP or WP Rocket is causing the problem as it is working for other sites?

These sites does not look all the same. There are for sure different settings.

But what can causing the problem with this Flash Of Unstyled Content, if not the theme or a caching plugin?

The only changes I have made were updates.

It's usually the caching plugin.

Have you tried disabling WP Rockets for that site with the issue yet?

You will need to take some actions to identify the problem.

It's definitely not the theme - you can see that it isn't happening in any of our sites here:
https://generatepress.com/site-library/

Yeah, I am not saying that it is only the theme. But I have wp rocket on about 18 sites with different themes and had never such a problem.

That is why I open a support ticket. And I have copy the answer above.

Maybe it is a combination of theme, settings and cache settings.

But I don´t know what to do. I have asked here the GP support and I have asked the w-rocket support. But I have still this problem.