5th wheel receiver hitch latch not completly closing

I suspect that the truck has rolled forward a bit when you put it in park. Make sure the truck is lightly pushing against the kingpin when putting in park. I have seen a few times where the truck would roll forward a bit each time is was put in park and required me to have the wife hold it against the kingpin while I locked the hitch. If you have clam jaws instead of a bar, you can close the jaws first and then back in. They will spring open and close without assistance.