Bad road = blocked tailgate ... ?

After a short trip on a riled mountain dirt road, the tailgate could not get opened without brutal force. After a few forceful manoeuvres it now OK. It seems that the tailgate slightly shifts to the passenger side, and jammed the lock on its left. The truck is new, is it a manufacturing defect?, any similar experiences?

 

How do the gaps between the sides of the tailgate and the bedsides look? Are they square? You said it shifts to the passenger side…is it hitting the bedside? Is the issue just in the hinge, or is something impeding the piston that lets the tailgate down slowly?

 

Thanks for your questions. I double checked, measured the tailgate gaps, on the side and at the bottom. Everything seems square and fine. The issue was not the piston, as I the other day had trouble to unlock the tailgate. Here is a picture of the left lock striker, showing use on its the rightmost end.
The only thing I notice is that the hinge on the R side, is slightly wobbly. This hinge allows to pul up the tailgate when it about 45° from vertical and unhook it. However I did not drive so steep up!

 

Glad it did not happen again, for more than a year.