You are likely on to something here, while radiant barrier is a great product when properly installed, herein lays the problem at least what I see is it is almost never correctly installed.
Take a look at picture #4 of your post at the far view of the attic. It appears that the barrier is installed on the hip members which are perpendicular to the ridge vent, preventing reflected heat to be vented.
Also while not shown in your pictures does the home have a continuous soffit vent?
Properly installed vapor barrier must have a fresh air intake at the bottom and an exhaust vent at the top of each truss bay that is covered with the barrier, If not the hot air is reflected back to the roof, which can shorten roof covering life and in extreme cases break down the adhesives in the roof sheathing
Still doing research…and found this. Any opinions and should radiant barriers be wrote up.
“A better technique but not without its technical challenges is to attach the radiant barrier to the bottom of the roof rafters, the structural members that support the roof sheeting. This creates a chase between the sheeting, the rafters on each side and the radiant barrier. This chase can be used to provide a thermal chimney where cooler air can be drawn in at the bottom, preferably from the outdoors and not from the attic, and then this air is warmed and it rises and exits to the outdoors at a ridge vent at the top of the attic. Without this controlled ventilation technique, the result of putting radiant barrier at the bottom of the rafters would be the same as applying it directly to the sheeting. Obviously, this controlled ventilation technique needed is also not practical to retrofit to existing homes. Further, any application of radiant barrier up at the roof deck has little or no savings or impact on comfort during winter months. Airborne dust moving with the vented air up this chase is going to be deposited on the reflective surface more rapidly than a single layer over the insulation. One other consideration is the overheating of shingles. Shingle manufacturers are now limiting or voiding warranties where RBS is installed under the roof decking.”
Actually, that’s what’s shown there, Tom. In photo #5 you can see the space between the radiant barrier and the underside of the roof sheathing. If the barrier were touching the underside of the sheathing or if the space was negligible it would void the shingle warranty and you would expect to see accelerated shingle deterioration.
If there is “plenty of ventilation” then the temperature of the thermal chase (enclosed rafter bay) is not an issue and heat is not effecting the shingles. The measurement you want is the temperature in the chase VS the temperature outside. The fresh air intake at the soffits has to be in balance with the hot air exhaust at the roof peak.
Mark has a good point in mentioning that anywhere truss top chords connect to a hip at the top, instead of to the ridge, that bay will not be connected to a ridge vent at the peak and the soffit vents will be ineffective in ventilating the roof structure in these areas.
From your photos, I don’t see a problem. Very minor cupping and I can’t see patches of missing granules. If the granules are in the gutters, they’re probably hitchhikers.