PO/ PR Charge account not defaulting

We are in 12.1.3. In one of the Test Instances  Suddenly  PO /PR Charge account is not defaulting  for   expense lines and we need to enter the  Charge account manually. As per the defined functionality For Purchase requisitions ,  Charge account should default from  Employee's expense account or from  Expense account  rules. For Purchase Orders, if we enter the 'Requester' Field, then Charge account should populate  from Expense rules  / Employee expense account. Same is working fine in other instances.

Any help  si appreciated.

Thanks

Jagan