I'm aware that there's sometimes an issue with post titles not being re-populated if you hit preview or go to another page, and then hit "back" to go back to your post.
However, I've never heard of titles disappearing while you're on the same page. There's nothing in our code that I'm aware of that could make that happen.
To explain: When you go to post, your browser receives data from our server when the post page initially loads, and sends data to our server when you submit the form, by either previewing or posting. But aside from that, no data is being sent to or from the server while you're just sitting on the post page typing into the form. So there's no mechanism to make a post title disappear.
That's not to say it can't be done. I could definitely create this effect by forcing text to disappear from an input box after a certain amount of time -- but to do so would require some very specific coding at our end, which does not exist (because that functionality would be of no use to anybody).
All that said, it could still be something at our end. I'd be curious to know if anyone else has experienced this. But given the above, my initial speculation is that it's device specific and this is something to do with your personal configuration. Maybe ad blocker/content blocker/privacy settings of some kind?
Edited to add: I see some people have experienced something similar, but I wonder if we're all talking about the same thing. To be clear, refreshing a post page while you're in the middle of a post, or leaving the page and then using the "Back" button to get back to it, can definitely cause the title field on the post page to be reset. But I'm unfamiliar with the issue occurring if you never leave the page. Do you literally see it just vanish before your eyes while you're typing?