As of now I have received the messages of two users of my app Speech Central that it doesn't read the text for them on iOS 13. After researching some more on the internet I found two more posts from other developers who report that some of their users have similar problems, and from the feedback on those posts it seems that also few more developers are aware of the issue/have the same issue.
This doesn't seem to happen frequently, but if the text to speech in the app you use doesn't work (some apps even crash) on iOS 13 try to restart the device, one user has confirmed that it has resolved the problem for him, so hopefully it can help someone else too.