I have experienced similar of that. I directly put it in steemit. I composed it for almost 2 hours. I stopped to take a short break. My phone darkened because it was idle for more than 3 minutes. I tap it twice to operate and continurle writing, but it didnt work instantly, so I tapped it 3 times, and the 3rd tap clicked the CANCEL in my post, and everything was gone. I slept and very mad at myself...