Scenario:
The expense sheet submitted by a user goes to the old approver who is no more the expense sheet approver for the user and doesn't go to the current or active approver or supervisor updated under the user profile.

Cause:
The expense sheet comprises of expenses that were incurred at the time when the old approver was the active expense approver for the user. Hence the expense sheet had gone to the old approver for approvals instead of the current approver.

Resolution:
Backdate the new approver's start date in the Supervisor section, under the Advanced tab of the Edit User page, to a date that is prior to the expense incurred date.