Renewed contract lines are not being created with correct billing streams

We have a contract for one year with multiple products all for one year and all for the identical effective dates and all products are on monthly billing.

Occasionally customers will want to purchase additional licenses, so we update the original instance to reflect the new license count, example from 5 to 8.

We then add a new line to the existing service agreement for the balance of the contract term for updated instance quantity and flag the line to renew the full duration and terminate the existing line.

We bill monthly successfully for the balance of the contract term and the contract renews with all lines for 12 months but the billing stream for the line that was on the contract for 5 months does not have 12 billing streams as we would expect, it has 5 billing streams like the original.