Considering the plate is mounted via nylon bushings, I'd agree that "some flexing" would be normal.
However, any cracks or truly distorted metal would be a cause for concern.
You've documented your situation with Mor/ryde. Now check the pin box before and after each tow. Any changes, especially, cracking, warrantee claim!
TT 2015 19RD "TheJayco"
TV 2003 F-350 "Montblanc" - Housebroken chore truck
Sitting in The Cheap Seats.
And proud of it!