Comments get deleted when trying to post

I have tried to google an answer to this, and always seen things like "you don't have enough karma" or "you have not been a member of a sub long enough"

But none of that applies. What the hell is with the phenomenon where very often when I type out a reply for a post, and then hit "comment", my writing just gets totally deleted. If I write if for the second time, it usually posts. Sometimes I need to take a third round.

I've had to get into a habit of copying (and then after a failure pasting) everything I say, And sometimes I just forget to do it. It's such a pain! What do I need to do differently for reddit to not randomly delete my replies??