Flickering sidebars and pages

I dont know a quick way to regerenate thumbnails unfortunatelly. But forget about it, lets reference this page
https://analitik.istanbul/hakkimda/

no flickering at all, so ? this is useless in this form. If I add these custom html and enable very basic plugins, it will start flickering.

Adding a html widget into sidebar or adding a code on a blog post with a highlighter plugin makes the whole things flicker, this is what I am able to find.

The reference page also has this:
https://www.screencast.com/t/PW3FySepp0r

Which reference to this image:
https://analitik.istanbul/wp-content/uploads/hg.jpg

And it doesn't show in Chrome:
https://www.screencast.com/t/WUgLfzPRAOD

Can you create a new sample page without this issue? Then activate the plugin one by one so we can try to tell if any of them is causing this?

do u see any issue with this page?
https://analitik.istanbul/power-bi-nedir/

if u dont then I'll start activating plugins.

I don't with Chrome:
https://www.screencast.com/t/ceRrZxd8

But there seems to be some issue with title loading before logo image on Firefox:
https://www.screencast.com/t/7eQiHgx0962

Are you able to have a quick chat with your host and make sure there is absolutely no caching or anything from them?

It's a virtual machine on Azure with ubuntu + nginx + wordpress, not hosted by someone else.
I am not sure which should be loaded first.

I am activating Ultimate Shortcode plugin, one of the vital ones for my blog, pls check it.

I see no issues!

I have added just custom html widget, without activating any other plugin, and now it flickers heavily!

Are we sure it's not the font icons on the page? They can take a second to load, which can lead to jumping as your video showed.

What if you remove some of the icons (home in the nav etc..).

removed home icon, search icon is due to settings in customizer. still flickering.

as soon as adding html widget page starts flickering. without it, it was all fine, makes me think it is not related with icons, my 2 cents.

I can provide you username/passwd if u'd like to examine it by yourself.
just give me your email.

The only flickering I'm seeing is the home icon.

Which custom HTML widget is causing the issue?

Newsletter HTML Widget

hit refresh or logo several times, u'll see sidebar and menus are flickering.

check this page too pls and hit refresh several times, very heavy flickering.
https://analitik.istanbul/power-bi-nedir/

What you're seeing on that page is your shortcodes ultimate items loading. They're using javascript to hide the text until you click a heading, and the javascript is taking a second to initiate causing the content to show briefly.

If you temporarily remove the shortcode from your content, you'll see it goes away.

It is not completely gone when I disable it, still slightly flickering. See recording pls.

Reverse is also true, with Shortcode ultimate is active,there is no flickering. When I add html widget, it starts flickering. I am a novice user, if the problem is related only with SU, then I should see some heavy flickering too, but I do not?
https://youtu.be/tx3IOKY9WgQ

That's just the sidebar loading after you refresh the page. Your page is loading very fast, so the only part you actually see refresh is the sidebar, as the sidebar HTML is at the bottom of the page.

No matter what you do, there will be some "flickering" or "loading" when you refresh your site. This is the same for all sites (regardless of theme, plugins, or even WordPress).

So what should I do as a result?
I need to use SU, it's one of the vital plugins for my blog. I am also very happy with GP and your support.