Hi and thank you for such a quick answer. I know I should have checked with a stock theme first, but I noticed the problem when the traffic was quite high on my website and didn’t want to ruin the users experience by changing to another theme. It seems that 2015 theme is fine, so this is theme related, you were right.
However, the link you gave me has nothing to do with my problem, that is a matter of CSS, not a matter of permissions.
