From our main site,
however your user should be able to use iOS 9.36 per these commits by @j.jaffeux
https://meta.discourse.org/t/ios-9-3-5-and-blank-page/123688/16?u=dax
If your Discourse site is up to date there may have been a regression.
That’s said, since that is an unsupported OS, if there is a trivial fix, we will get it sorted but if anything is looking complicated we will fix it so we properly display a “browser not compatible” message on the page.