If the roof side seam caulk is not properly maintained, the fiberglass cap pop out of the groove just as you describe ...nothing to do with the heat pump.
Paul ... was Fulltimin... now HalfTimin!
KE5LXU, SMART, WIT, FMCA, Good Sam, Escapees
'03 Winnebago Ultimate Advantage 40E / '17 Jeep GC Limited