That's because when you type you can sometimes refresh the page mistakenly which happens the most when I make use of mobile to post. Like I mean the drag to refresh can be frustrating sometimes imagine writing a whole block of text and then you lost it with just a drag from the top.
That happened to me many times using mobile, while its okay on desktop since it still remain even after an accidental refresh but it is different on mobile browsers. But fortunately, i used to use the draft/preview feature so opening another app just to write a post isn't an issue to me.