Oak if the ball is not properly centered under the hitch (on a ball hitch) the latch may latch ABOVE the ball instead of under it I have seen it happen many times.. I tested for it and fixed it (Usually I knew it right away).. I do have an advantage in that I've been hooking up trailers ever since I was about 10 years so I know how it should look and feel when it latches..
But it is very possible to have it latch normally or appear to only the latch is ABVOE the ball, not below it, so the trailer simply lifts off.
