I have the exact same problem on my iPad pro, my iPad air two and my I phone 6S plus
Problem does not exist if I am on 4G or LTE – it only exists when I'm on Wi-Fi, and it seems to be DNS look up failures
Many sites have ads or other things that require a browser actually have to perform 10 DNS lookup's just to load one site, Safari likes to load the whole page before it bothers to display it which is kind of annoying – it really should display the side as it receives the data unless there's a reason not to
I have tried using Public DNS servers like Google, the DNS server on my router, my ISP DNS server, and finally I started up a windows 2008 are two server and then Oracle VM virtual box on my windows 10 64-bit machine... I thought it may have been a problem with my router over loading it with all of the DNS requests and stuff I have in my house – I have a lot of tech. I have most of it wired with only the mobile devices on Wi-Fi...
my router runs a DHCP V6 server in stateless mode using Twc Dhop-pd also , but I run the on the DHCP service on the router so I can manually assign IP addressEs in 2 instances. Otherwise in stateless mode devices can figure themselves and report their settings to a DHCP V6 server and a DNSV6 OR DNS V4/V6. My Windows server "in a box" handles all my IPV4 DHCP requests and all of my IPv6 and IPV4 for DNS requests
This did help things a bit but the problem is Safari because if I load Google Chrome browser on my iPad or iPhone or use a fantastic browser called iCabMobile ( which is a fantastic browser because you can tell it to lie to any website and tell it that it is any form of browser out there so you don't get mobile sites – this is handy on the iPad )
when I use non-Safari browser's, DNS look ups properly and websites load fast. I do have an occasional glitch in my iPad Pro which is probably a hardware issue where once every few days it just can't access any networking not even cellular data. I have to put it in airplane mode for 10 seconds and then turn off airplane mode and everything works fine – it's either a hardware problem more software bug for the pro they have not figured out yet
Does this here because I do not think this is an iOS or OS X issue – I think it is a Safari issue and resetting all of the data on my iOS device for my Safari browser has no effect on this issue, plus that's the only time I'm ever going to raise that issue because it erases my cookies which I actually need for variois sites as keychain is not enough has some sites won't let keychain save my username and password. I also have true key for my PC and for my iOS devices so that's another way to keep my passwords remembered safe and secure, but I really think safari is had problems on any operating system platform for quite some time
Think one way to solve the issue would be to have an option in Safari to when you load a webpage that it doesn't load data from any other webpages. Course that will cause issues with embedded pictures or other and embedded data from other websites but that should be up to the user..that's something I can control and icabmobile - which also helps to block advertisements because of the browser doesn't load or look up any DNS IPs from the main site, then it will greatly speed up loading times, and this can also be the problem with safari in that if you go to Lotus site that has multiple advertisements and if anyone of them timeout, Safari will not load the page – where it may take 2 to 3 minutes to load the page because the timeout values reset incorrect
Or we could even have an option that limits DNS lookup requests per website domain that we are trying to load to anything from 1 to 50, and if you set it something like three that should be sufficient to load most any website