I have never used grease on a ball because I don't want the mess. It's an option but not necessary.
The hitch will stick on the ball occassionally. Just lower it to take the pressure off. Cycle the latch and try again. If that doesn't work, like posted above. Without pressure on hitch, take parking break off and see if TV will move an inch or so. Don't drive with jack down at all. And maybe this goes without saying, but don't stick your fingers under there to try to release the latch even if it looks like there is no pressure on it.
Last question you had, always undo the latch with no pressure. on it. have the tongue weight on the TV, not the trailer. Release the latch. Raise the tongue.
Photos would help to diagnose your exact situation.
