Amic58

Thanks David for replying. Indeed, it is very odd issue, that appeared out of nowhere. I contacted my provider through their live chat, but they said that they don’t know what to do. Because on live chat they might be a little rushed, I will write them mail and see what they respond. If nothing changes, I think I will change the provider.

Also, is it possible that the fault is on provider’s side?
Since the problem I made a new database, reinstalled WordPress etc., but nothing worked.
I tried to insert YouTube video link on the web with different provider, and everything worked normally.

Hello Mika,
sorry, I removed the posts, but here is the new one, with all steps that were suggested here: https://igamers.cz/test1/

About the sidebar, everything worked even by posting just the URL https://i.imgur.com/3Fm4SI2.png. Interesting thing is, that when pasting Vimeo video, on the sidebar or to the post, it works – see here https://i.imgur.com/TZYN8Ia.png .

I appreciate that you tried to help me. Hope somebody else will know the answer to this. Thanks again!

Hello James, sorry for not saying anything for a long time, had lots of work.
So I asked my hosting provider about turning mod_security off, but they said that they don’t use it, only mod_deflate and mod_rewrite.

Hello, here is the link to the page after updating to WordPress 4.4.2. It didn’t help.
Is mod_security server-related? I will ask them about turning it off soon.

MarkRH: With that iframe tag, it works, but it doesn’t auto adjusts the video for my site. Also what interests me is, that the normal method, just pasting url, doesn’t work anymore.

Here it is: https://igamers.cz/test5/

I found out that in HTML editor there is this

words above

[embed]https://www.youtube.com/watch?v=LS-VPyLaJFM[/embed]

words below

But in Visual Editor, there, instead of video, there is written “Failed to embed”. Example here: https://i.imgur.com/haeAdZl.png

Here is the link to a post with working Vimeo video: https://igamers.cz/test4-vimeo/
It works even without putting [embed] tags.

Unfortunately, no effect. https://igamers.cz/asda/

No, I am not. I disabled all plugins one by one, to see if it made any change, but nothing.

Here is the link to the site. Actually, if you look to the left side, where there is “Nová videa z Gamers TV” (translates to new videos from Gamers TV), you can see that under it is only a link, not the video.
And here is the link to the Test2 page, with the latest suggestion. As you can notice, the link is clickable, but the video doesn’t appear on the site.

Thank you for your suggestion, but that didn’t help either.
Here is the picture: https://i.imgur.com/ELSuUDP.png

I deactivated all plugins, but that didn’t change anything. I also switched to different theme, but that also didn’t do anything! Wow, I really don’t know what to do..

I put it into the HTML tab and saved it, but nothing changed.