On some web pages in Safari; web views in apps; and some pages in apps, you may find that VoiceOver focus will spontaneously ‘jump’ to a different UI element.
This behaviour does not appear to be widespread, but can make navigation difficult and confusing when it does occur.
One example of this behaviour in Safari can be seen with Google search results when using the VoiceOver rotor to navigate by heading.
In the worst examples of this behaviour, you may find that it is impossible to activate a link or a button because VoiceOver focus will not remain on it long enough. In these cases, focus jumps instantly. Some people have reported that locating the item by touch has enabled them to activate an item in these cases.
An example of this behaviour in an app is the App Store app. In this app, if you go to the Today tab; double tap on “My Account”; and then double-tap on your name, the contents of the ‘Account’ page and many that it link to are extremely difficult to navigate due to VoiceOver focus constantly ‘jumping’.
Note that the examples given above are just that, examples.
In practice, you are likely to encounter similar behaviour in different apps and on various websites. And, in the case of website, not only when navigating by heading.
It does appear that the issue is related to actionable elements, such as links or buttons, as we are unaware of any situations when VoiceOver focus will jump when placed other types of UI elements.