I can confirm that this happened to me once this month and several times in the last 6 months. The solution was to log out, then log in and the problem was solved.
Same here, I usually experience it once in a while whenever I experience it I either put my device on flight mode then remove it on flight mode , because most time is due to poor connections.
And I don’t usually repost the post once after it occurs I will have to save the post on draft first then I will refresh the page see if my post went through before taken any action to avoid double post .