@Inna22
Inna, always copy your text before you hit Reply or Submit. I know that sounds a bit like the pot calling the frypan black, but it is not just those odd glitches that crop up from time to time! Sometimes I will get called away in the middle of a post and when I come back and complete it, I hit Reply and a red field at the head of the post tells me to refresh the page and authenticate, my time has expired.
Like you, I learned the hard way, particularly where DM was concerned, don't know how many times I got hit with the 'Oops, can't send your message just now'! and the message just disappeared into God knows where.
I would never start a post no matter how short (not just here but on other platforms) and attempt to send without copying first.
The thing that I find most ironic, if a post is going to fail to send, it's always the one you put that extra time and effort into.
Cheers..........Rob