right here:

The Pentagon said the weapons they would send to Ukraine had a failure rate of 2.35 percent or less, far better than the usual rate that is common for cluster weapons.

But the Pentagon’s own statements indicate that the cluster munitions in question contain older grenades known to have a failure rate of 14 percent or more.

here is the original document they are quoting from. page 31/32 (35/36 in the .pdf's numbering) states that:

U.S. ammunition stockpile sample testing also indicated that DOD has experienced past problems with submunition reliability rates. For example, in 1990, testing of artillery-delivered nonland-mine submunitions identified two lots that had duds in excess of 40 percent. According to a testing document, one way to compensate for this high dud rate is to increase the quantity fired. Instructions contained in the testing document were to “Notify the user of the increase in submissile defect rate so that he can make adjustments in the tactical employment plans.” The July 2000 Army study of dud rates for ammunition reports that the dud rate for artillery-fired M42/46 submunitions is over 14 percent.

the Pentagon's actual, data based estimate (and not its uh, lying) correspond well to other data reported by groups such as Human Rights Watch (which have routinely found submunitions to have rates like that across the board), and specialists in the field who anecdotally report rates of as high as 30%.