Change the source from the LAN interface (eth 0/1) to the MFR interface or Loopback address (if applicable). Below is a netflow config with a MLFR from a Cisco 2821.
<route>#sh run | i flow
ip route-cache flow
ip flow-export source Loopback0
ip flow-export version 5
ip flow-export destination <IP> 2055
I Concur, the best practice is to use the LB interface as the source
behavior you've described corresponds to quite common mistake done in device settings - exporting flows interval is not set to 1 minute. For Adtran device you should includeip flow cache timeout active 1 to device config.
For more details and config examples please see SolarWinds Knowledge Base :: NetFlow Interface resource(s) show utilization peaks higher than NPM utilization or higher than the interface bandwidth.