This is one of the most frustrating and cryptic error messages thrown on the web today.
There are legions of articles which suggest playing with various setting on iOS, but in reality don't bother with them.
Basically this message means Safari crashed (like Chrome Aw Snap, but without any extra information or the ability to provide feedback),
One of the most likely cause for this to happen is when Mobile Safari runs out of memory,
in my current case it relates to a crash after attempting to take a photo from <input type="file">
You can find crash logs under Settings -> Privacy -> Analytics -> Analytics Data (iOS 10)
As far as bug reporting goes, Apple operates their own event horizon with their radar system, but you can try a few of these public resources, http://www.openradar.me, https://bugs.webkit.org/
Meanwhile, other major browsers make developers life easier with a more open approach:
- Chrome's public bug tracker, their developers actively engage with bug reports
- EdgeHTML issue tracker, they are also very responsive, you can report IE11 problems too but unless it's a security problem, they will reject it as won't fix.
- Firefox Bugzilla, depending on the problem you might get some response