Some youtube videos won’t play

This is your HTTP response headers:

$ curl -I https://www.xxxxxxxxxxxxxxx.fr/cd-alea/for-their-love-other-lives/
HTTP/1.1 200 OK
Date: Wed, 10 Jun 2020 09:28:10 GMT
Server: Apache
Link: <https://www.xxxxxxxxxxx.fr/wp-json/>; rel="https://api.w.org/", <https://www.xxxxxxxxxxxxx.fr/?p=40108>; rel=shortlink
X-Content-Type-Options: nosniff
X-Frame-Options: DENY
X-XSS-Protection: 1; mode=block
Referrer-Policy: no-referrer
Strict-Transport-Security: max-age=2628000; includeSubDomains
Expires: Thu, 11 Jun 2020 09:28:10 GMT
Vary: Accept-Encoding
Content-Type: text/html; charset=UTF-8
Via: 1.1 alproxy

You have: X-Frame-Options: DENY
If the video is loaded from an iframe, it will likely get blocked.

Sorry, it was on “Same origin” in first test (and I put it on Deny because I must be a little dumb :-).

I changed it on No and the problem is the same.

This is what I see:

Should there be more videos on that page? I can only see 2 iframes in the source of the page.

The firewall won’t block videos, but if you setup some “HTTP response headers” policies in the “Firewall Policies > Advanced Policies”, your browser could follow NF instructions and block them.
If you see the error once again, open your browser console (CTRL + Shift + j) and look for blocked content. For instance, here’s an example of blocked content:

OK, it was Referer-Policy that blocked the streaming. I deactivated it as I did not find any setting working.