Why the tax is not getting calculated for some of the po lines in Pogress claim invoices in r12

Hi,

There are 3 progress claim invoices where the tax is not generated for few po lines. the rest of the lines tax is calculated. We have checked tax setups and tax at po level and all look fine. there were no past invoices for the specific po line which tax is not generated and now from the specific invoices those lines are fully utilized. I'm talking about the same po different line. so basically the issue is with line 20 to 24. and these invoices have been paid and accounted but now only they have identified the tax variance.

We also found that those lines have been closed and after that they have done some changes to the invoices. so we did testing for a different line where they raise progress claim and close the po. but at the moment the invoice is auto generating the tax is calculated. we don't need to manually go and take actions to calculate tax.