In Safari for iOS you can't set the height of an iframe. This has been available since the <iframe> tag was first introduced in IE4 I believe.
There are a number of hacks to remediate this such as using a div with overflow scroll which encapsulates the iframe, or using an absolute positioned wrapper on the contents of the iframe.
Safari is always lagging far behind, and that's just the list of technology here, it's difficult to list all the nonsense tricks you have to do to make your website specifically work on Safari when it works on just about everything else by default. Personally I spend about the same time on Safari support as IE11 support. Has Apple gave up on Safari?