iMessage Unsent Message Text Lost
When I (1) open a new thread in iMessage and (2) have not yet specified a recipient but (3) have started to enter the text I intend to send but (4) have not yet sent it and (5) an iMessage from anybody comes in to my phone and (6) its notification banner appears on my screen and (7) I tap the notification to see the message and (8) thereby am delivered to that message thread ~ then (9) the result is the loss of any text I had composed forever, because (10) on exiting the thread for the incoming message, (11) the list of iMessage threads does not include an entry for my unaddressed message thread, and (12) selecting to start a new thread takes me to a fresh empty new message.
Presumably the loss of data is why you can only cancel from a new thread if you have not yet sent a message to establish it as a thread; but the banner-tap on an incoming message evades that restriction, taking you out of your unfinished work without having canceled.
Another situation where you may lose data is when you use the camera app to select a photo to be emailed and switch away from the app before finishing your writing in the email to go with the photo. When you come back to the camera app it appears as if you had never selected the photo and entered text. In some cases selecting the photo again and again selecting it to be emailed will surface the unfinished email but most of the time you are flat out of luck.
As you can see I am loquacious to a fault, a big fault, so these events have at times cost me dearly, especially when I was composing some quasi-literary essay for a friend. I realize of course that iMessage is not designed as a place for such windiness, and for most people there is only an extremely brief time window between when they start a new thread, tap “hey bro don’t blow up my phone” and send, thereby establishing the thread. So this is very much an edge case. Ditto the camera app emailing a photo situation ~ most people send the image with no text or very brief text like “check out Mom at the beach lol” not a 500 word freak-blab recounting her agoraphobia, noting her resemblance to a young Winston Churchill, and then speculating whether Dad’s passing has anything to do with her overcoming her phobia.
I have learned it is best to copy and paste into the Notes app any time my iMessage composition begins to scroll. Likewise if the cam-app-spawned email, which never is autosaved as a draft, shows a scroll.
iPhone 6s Plus, iOS 12