EX Approvals with HR Supervisor and EX Rpt Mgr

We use both the HR Supervisor and the EX Rpt Mgr approval routings for Expense Reports. The initial approval is the HR Supervisor, then if the report is over certain dollar thresholds, it gets routed to the EX Rpt Mgr. If the report is under the dollar threshold, the HR Supervisor is listed as the additional approver and it is Auto Approved. Occasionally, instead of the HR Supervisor being the secondary approver and auto-approving, the report gets routed to the HR Supervisor's supervisor. We can not figure out why this is happening. The report is under the dollar threshold and the Ex Report Mgr/Secondary Approver is not the one in the Approver Assignment for reports over the dollar threshold, instead it is routing to the person listed as the HR Supervisor's supervisor. Does anyone else have this type of setup and possibly seen this issue?
Thanks!