If you place a plain text test file in the .well-known/acme-challenge folder ( such as .well-known/acme-challenge/test ) can you get the plain contents in a browser ?
You appear to be using a redirect for coutelleriemarcin.it ( using ovh ?) to coutelleriemarcin.be which is placing html code in as a redirect in frames rather than simply providing the data from the website.
I’m not familiar with OVH redirects. Are your other sites ( which worked ) redirected ? if so, what’s the difference in the way they are redirected and the way this one is redirected ?