It was a color application chemistry issue. It is a fully known issue for Uponor, and the reps and Uponor are handling paying for correction. That is the facts as I have been involved as a licensed plumbing contractor/ middle man helping customers.
The first issues of leaks seemed to be limited to the color applied Uponor PEX, and the elimination of the colored Uponor from sales seemed to back that up, but now even the white pipe is showing up with cracks and pinholes after 5 years.
Someone posted pics (might be on this forum) of some pieces of white pipe badly yellowed and cracked and other pieces from the *same* house were clean white. Both samples of white pipe came from the same house but only some parts had the yellow and cracking. The youtube repiper the poster above linked to has about a dozen videos that show damage to both the color applied pipe *and* now white.
Take a look at this segment:
He seems to think it's a chloramine issue (and indeed, it may be a contributing factor), but to me, seeing some pipe damaged and some pipe looking like new from the same house seems to indicate a batch issue contribution as well.
Hopefully, this will all come out soon one way or the other.