I'm trying to up-vote Q&A for "Why we're not customer support for [company X or product Y]" using SE app (1.3.1) running iOS 9 beta 1—get an error about being unable to do so with my account, to logout and try again; did so, still can't, was told by the app to tell you on "meta". I was just able to perform the action using El Capitan, however. And voting works for all other questions so far.
We support current and previous versions of all browsers with some reasonable amount of market share, but not beta or development versions.
Source: Which browsers are officially supported, and what else do I need?; emphasis mine.
iOS 9 updated many networking APIs and the list of known issues on the developer release notes for the first beta is long, even without developers providing feedback and reporting bugs yet.
Whilst it may be a bug with the SE app, it is also likely to be a bug in iOS 9, which may be fixed for final release. There's no point adding a workaround to an app just because something doesn't work quite right in iOS 9 beta 1, which isn't even the public beta yet.
Perhaps when iOS 9 public beta is released, pointers can be made towards features that are broken as it is likely that there are no more serious bugs in iOS 9, but iOS 9 has only just had its first (private) beta release.