It's not 'GPD Taxable', is it?
Just spoken to JPAC EC having had the same issue for 3 consecutive payslips - they referred to an e-mail from the 'back office' stating that the GPD Taxable was a known problem affecting "lots of people" (their words not mine) and that a 'bulk fix' was going to be applied on the AUGUST pay run i.e end of Aug. They had also been instructed not to raise any SRs against the issue.
Good luck
BG