I double checked, and I don’t have any issue concerning loopback though,
only the one I mentionned earlier.
For .htacess, I used W3T Cache plugin which add some custom rules in it.
Even before adding this plugin, I had the error, and the only custom rule I had was :
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://www.my-site.fr/$1 [R,L]
I tried another time by deleting these lines btw, same result.