I think it is ssl related. Because other sites i created which uses the same certificate (royagterberg.nl, kimagterberg.nl, opelstrijders.nl, gpsforce.eu forum.megane-rs.nl and megane-rs.nl) are also not showing on iPhones. I recently renewed my certificate and I did that with StartCom. There’s been some news about this CA because since 21 october 2016 startCom is no longer a trusted CA. Every certificate released before this date are still trusted but as I mentioned above. I renewed my (multi domain) certificate this january. Maybe that’s the cause of the problems.
I’m trying to find an CA that offers cheap multi domain certificates but it’s hard to find.