Scheduled Posts not actually posting

This has been an issue that has struck repeatedly, it struck again today. A scheduled post did not actually post at the time it was scheduled. When I checked the post the time on the post was counting up as if it had been posted (Scheduled at 12:00, checked at 12:02 and showed 2 minutes, 12:04 showed 4 minutes).

Had to delete scheduled post and post it manually. This has happened a number of times.