Welcome to the forum,
Wow what a frustrating problem! Definitely sounds like a thermal expansion issue.
Which the dealer is not likely to re-create. Perhaps you can inspect the door edge / frame and find where there has been metal to metal chafing. Perhaps an overlap near the striker plate and latch assy. Try barely loosening the HW screws and opening and closing it softly aligning it then snug them again. Of course the moving parts are lubed correctly. Try a little chap-stick or Vaseline on a q-tip on the back of the striker. Look for scoring on those parts. Those doors are pre-hung so the frame could be in a bind also.
Once had a coach that had a residential dead bolt on the door that worked smooth as butter normally. One very hot sunny day I experienced that sick feeling of being locked out. The key turned but the bolt would not budge. After an hr. or so I contemplated which locksmith to call. My intuitive neighbor on a whim grabbed a bag of frozen green peas from her freezer and held them over the latch / lockset for maybe 5 min. as I scoffed kicking dirt. Open say's a me she chanted and it click over like butter. Go figure! Make a believer of me.
J & J, DRV Suites ES-38RSSA #9679
GM Denali, 3500HD-Max, 4x CC, 8' DRW,
EZGo-TXT, Clubcar Precedent