Even with the wheels chocked if the side pressure is not removed from a sharp turn backing in, it can slide the tongue jack off a wood or plastic block when it’s raised off the ball…
I have had this happen myself years ago and subsequently heard of it happening and the owner didn’t have his feet out of the way causing tragic results…
I was also sitting under a guy’s awning on a level concrete pad in FL… the trailer had been there more than a year (maybe two) when all of a sudden due to movement inside there was a loud bang and the trailer moved forward… it had the 4 corner jacks down with blocks of wood (dimensionally to high and not enough surface area IMHO)… apparently the guy hadn’t checked the air pressure in the tire and leakage overloaded the jacks… he used pieces of 4x6 under the jacks with the 4 inch being the surface side and all running the same direction… effectively making them as much like a roller as a block…
You just can’t be to careful…