Any more so than with other materials?
CF has been used for the majority of forks for anything above the absolute most basic road bikes for at least the last 10 years, probably more, and you certainly don't hear of the breaking in droves.
Yes; for the reasons I've constantly stated in this thread. Marketeers and punters like to boil things down to simple, binary statements -i.e. "this is stronger than that, the end" - while the reality is often far more complex and subtle.
Load a short piece of UD CFRP tube in pure tension along the principal axis of its fibres and it'll probably have a comparable tensile strength to some steels, and will be a lot lighter - hurrah. Load these parts in compression in the same axis and while the steel will exhibit broadly similar peak stresses before failure to the tensile test, the composite will crush and shatter like a piece of raw plastic as the strength is in the fibres and they contribute nothing in compression loading; and even less if loaded tangential to the principal axis of the fibres.
The Oceangate Titan sub implosion is a perfect illustration of what happens when people fail to properly understand (or are too arrogant to to heed) material properties or basic engineering principles. Evidently Mr. Rush made the basic, over-simplified assumption that "carbon fibre = gud"; and made the literally fatal mistake of using this material in totally unsuitable manner.
While composite covered / filament wound aluminium pressure vessels do exist (and are disconcertingly light if you've ever picked one up) they work because of the enormous strength of carbon fibres in tensile loading. Take that same vessel and reverse the pressure loading so that it's now acting from the outside inward, and it'll fail at a much lower pressure. Further, compared to contiguous, isotropic materials like steel and aluminium commercial composite pressure vessels usually have a finite service life stated; beyond which they must be destroyed.. another reflection of the complexities and uncertainties inherent in the material.
Used correctly CFRP is indeed a miraculous material; however compared to metals it demends a higher level of skill, understanding and care at every stage - design, manufacture, inspection, use and maintenance..
You're absolutely correct that we don't see composite forks "breaking in droves" however I firmly believe that they're subject to a significantly higher failure rate than steel, while impending failure is a lot harder to detect and prevent. While certainly not an epidemic, if you look there are plenty of horror stories on the net about composite fork failure; many of which have resulted in serious injury or death.
There are also a few pundits on the net with a background in this field who inspect and critique composite bike bits; often with quite shocking outcomes. A good example is
Luescher Teknik; who incidentally builds and rides his own composite bikes so isn't inherently "anti" as some might suggest towards those who are skeptical of placcy bikes.
While the chance of being subject to a composite fork failure is probably very low, personally I feel this risk along with the other potential shortcomings of the material are not justified by the performance benefits it brings to the average, non-competitive recreational / utility cyclist.
Others obviously feel differently and of couse that's their choice; however it's irritating to see the irrational, ill-informed and hostile reactions of some towards legitimate criticism of the material they choose to ride.
