When using the swipe gesture to move through a active elements, you may occasionally find that VoiceOver suddenly starts to take 3-5 seconds to speak after you move focus to an item.
Once this behaviour presents itself, it typically becomes quite prevalent. Although it may not occur every time that you swipe after the problem first appears, it does become very frequent. For example, it swiping through a list, you may typically find that this problem occurs on every other item.
It has been speculated that this behaviour is a symptom of VoiceOver crashing and the delay in the speech is due to the time taken for VoiceOver to recover.