Dear Nandy,
The mesurement might have been changed with an old date( the change in the rental object might be recently or it might be in past), in the next subsequent change of the contract it generates cash flow.
You will get a better idea by checking the cash flow, due date, change documents of contract and rental object.
Still your issue is not addressed , paste the screen shots of cash flow, due date, change documents of contract and rental object. So that we can provide you more information.
Thanks and Regards,
Chandra