Path balance is the difference between the path loss in UL and DL. Ideally the cell sites are planned to keep it to 0. its planned keeping in mind the RF Losses of connectors, combiners, cables etc.
Path imbalance can occur due to hardware issues and their resolution resolved the case.
Path balance is only due to harware issue b/w trx to antenna.
VSWR or any loose connection is main reason for this.For rectification pls check VSWR,TRX test and end to end connectivity b/w trx to antenna port.