From the Cisco documentation:
Interface Index Persistence
This feature module describes the Interface Index Persistence feature introduced in Cisco IOS Release 12.1(5)T. This enhancement allows interfaces to be identified with unique values which will remain constant even when a device is rebooted. These interface identification values are used for network monitoring and management using Simple Network Management Protocol (SNMP).
Enabling IfIndex Persistence on All Interfaces Example
In the following example, ifIndex persistence is enabled for all interfaces:
router(config)# snmp-server ifindex persist
Enabling IfIndex Persistence on a Specific Interface Example
In the following example, ifIndex persistence is enabled for interface ethernet 0/1 only:
router(config)# interface ethernet 0/1
router(config-if)# snmp ifindex persist
router(config-if)# exit
This should resolve the issue.