Hard to tell via video how much movement is from trailer suspension and how much is pinbox flex.
With piece of tape place a reference mark on front of cap above pin box.
Take measurement from fixed spot on pinbox to reference mark:
1. when hooked up and all weight on hitch
2. when unhooked and all weight on front landing gear legs.
3. watch for movement when making transition between the two.
Shouldn't be more than 3/8" difference between the two readings
If there is then you should remove overhang panel and visually check pinbox structure, sidewalls for cracks, tears, bad welds.
Repeat hooking/unhooking while inspecting.