Soldering ball open after reflow and the slice analysis shows the ball open inside, what 's the problem of the soldering ball that might be?

Issue Des. :

Currently we find parts(EP3C5F256C6N)have soldering ball open issue , we have call support from third party ( CEPREI, Analysis lab) to do the Section(slice analysis) and red ink analysis

which indicate that the soldering ball is open inside itself. We also check our profile already which is meet the BGA spec as well, thus we need your analysis help .

Total input: 100 pcs

Failure QTY:44 pcs ( 43 pcs in 44 is manufactured in MALAYSIA, while the rest one is from Korea which we used before with no issue)

Failure rate: 44%

we find the failure mostly happened with the parts that manufactured in Malaysia which has MALAYSIA mark, KOREA's parts is mostly no problem,thus we think there should be something wrong with the soldering ball of the parts from Malaysia, see the detail from the picture and file attached.