Not sure it is related but I have some problems displaying our forum on an IPhone 6 plus.
Using safari on my iPhone 6 plus
and using Chrome on my iPhone 6 plus
my user agent using safari is
Mozilla/5.0 (iPhone; CPU iPhone OS 9_2 like Mac OS X) AppleWebKit/601.1.46 (KHTML, like Gecko) Version/9.0 Mobile/13C75 Safari/601
and my iOS version is 9.2 (13C75)
An other problem: When displaying the site using my phone in landscape mode The top navigation bar disappears.