The zoom magnification factor in iOS 9 has changed dramatically enough that I have to wonder if the new behavior is a bug that should be reported? Or is it intentional?
Zoom has an enabled / disabled state that is controlled in Settings, General, Accessibility. Once enabled, zoom can be turned on or off with a 3-finger double tap, and when on, the magnification factor can be adjusted with a 3-finger tap and hold, then drag up or down.
Prior to iOS 9, the magnification factor was stored in your iOS device, so that, when turning zoom on with a 3-finger double tap, the screen (or window) would zoom to the previously set magnification factor. Even after cycling power on your iOS device, turning zoom on would zoom in to your previously set magnification factor.
In iOS 9, this changed slightly. After cycling power on your iOS device, during boot, a small window appears on the screen with the words "zoom on" (not sure of exact words; a sighted person had to read it to me because it disappears before VoiceOver starts). More importantly, the magnification factor has been set to 1x, so it's not obvious that zoom is on at all. A low vision user used to the iOS 8 behavior will repeatedly perform a 3-finger double tap in an attempt to turn zoom on. All the while, it's already on, but with a magnification factor of 1x, there is no way to visually detect whether it's on or not, except for the afore-mentioned boot time text, which is in such a small font size that no low vision user can actually read it.
In iOS 9, the first thing you must do after boot is 3-finger tap and hold, then drag up to the desired magnification level. This is new and very different behavior from previous releases.
Was there some rationale behind this change, or is this a bug that should be reported? It is very problematic for low-vision users. Many have complained to me that "this is a bug".