Ok, this one is incredibly frustrating.
This is only applicable to the android app.
I've now wrote a long message to someone 3 times and each time I've wanted to review the message before sending and the slightest movement to the right whilst scrolling switches pages and discards the message. It took me a good 10 minutes to carefully write the message 3 times and I've still not sent it as lost it each time. Please fix this. Try it out for yourself.
Write out a private message to someone and go over to review the text by scrolling back up through it (make it a long message). Accidentally just nudge slightly to the right whilst scrolling. The side comes over and there's no way to stop it if your finger has left the screen. You can stop it if your finger is still on the screen but it happens so quickly otherwise and the message is discarded.
My advice is to either change the way this works or automatically save drafts of messages so they're not lost each time.
It also just happened reviewing the text for this feedback but fortunately this saves so I could come straight back to it.