EFT payments Undeposited Transactions postings

A client has a large balance in the undeposited transactions account, that has been mainly used for EFT payments from cash account customers via Bank batch.

Can someone confirm the usual postings I should be seeing for through payment in the clearing account (Undeposited Transactions), then recorded in the bank account and debtor payment allocated against invoice.

I am trying to identify the following scenario:

EFT payments via bank batch credit Undeposited Transactions, payment allocated to the debtor invoice but there is no corresponding debit in the Undeposited Transactions account, so balance is not cleared.

This has not been happening with all payments, the balance has been gradually increasing over time