Oddly enough, even aluminum ladders can have have some steel parts. The braces that hold open step ladders are one common place, aas are the feet of extension ladders.
I've never really had any issue, even in the harsh, unfiltered, high-altitude Nevada sun. Oh, I've seen plenty of faded ladders; it seems that the 'ugly' paint job I apply to identify my ladders also keeps the sun off the resins within.
The Werner flyer has me a little confused; I seem to recall the literature for at least one of my ladders claiming that the fiberglass part was encased in a thin PVC film for sunlight protection. Then again, most of my ladders are not made by Werner; Louisville and Green Bull predominate.
When it comes to fiberglass ladders, the fibers are the strength. Once they start shedding glass, it's time for replacement. They're no longer structurally reliable.
Keep in mind that shedding fibers can also be a sign that the ladder has been subjected to stress beyond its' limits. If that's the case, failure may be sudden and unexpected.