Voice Over speaking everything twice

iOS & iPadOS

Hi all,

My iPhone 5 occasionally gets into a state where voice over begins to speak everything twice. I am using the default voice namely samantha. In addition, if I swipe or carry out any other action, I have to wait for voice over to finish speaking. The voice does not get muted when a new action takes place.
A reboot fixes the problem but why does this happen? I cannot point to a specific set of circumstances that make this happen. The closest I can come is when I am swiping in the messaging app or am dismissing the search results in the phone app and the phone rings. However, there have been times when the phone has just gone into this state. The phone is running ios 8.4.

Other programs such as voice dream reader work normally when this happens that is, I can play books using synthetic speech without any double speaking.