Hi Atif,
I would ask them to post more consumptions to the addresses that are in deficit. If the posting went through, it would be either a configuration issue or some sort of system modification (BADI, etc). If the postings got stopped, than it would be so called 'error can not be re-produced'. It had to be at certain point of time some settings were changed (and later changed back). My speculation is it is the former case and it is caused by a system modification.
Regards,
Ming