Hi Anna,
I am not sure how below information helps.
Have you checked CJ40 / CJR2, how the plan values are built in that. Some years back we had issues like this, when we plan the cost in CJR2 and copy the same to CJ40.
Also check CJI4, when this plan cost was posted. After running the correction reports, if this is not solved, it can be a user error.
Regards
Terence