I have had severe problems with VoiceOver on my iPhone SE after upgrading to iOS 13. The voice became very unstable and finally stopped working after one or two days, Voiceover stopped reacting to gestures and the only way to fix this for a while was to remove all running apps from memory with the app switcher or just rebooting the device. I have posted this here around christmas and received several replies indicating that many other people, especcially those who use older iOS devices, were facing the same issue.
Here is the link to the corresponding thread: https://www.applevis.com/forum/voiceover-became-very-unstable-after-late...
Since that, I have - very hopefully, installed every upcomming iOS update, always hoping that the problem might have been fixed finally, but my hopes were disappointed each time.
However, the reason why I am writing this once more is that I have just found a solution that might also be of interest for some other people here. This week I found out that the option "captioning panel" in the Voiceover settings was enabled on my iPhone. I am not sure when this option was introduced to iOS, whether it was enabled by default nor am I aware of ever having enabled it myself,, but since I have turned the panel of Voiceover has become faster and more performant again and the voice problems have finally gone.
So if you are still using an old iOS device with limited RAM, check whether the captioning panel is enabled on your device and turn it off, which will improve the Voiceover performance clearly.
Kind regards from Daniel!