We have cisco 7609 routers in our network and we have configured it to send cache flow to information to netflow server. I'am able to see the devices are detected and necessary interfaces have been managed on the server,

The netflow server shows that it is getting flow from these devices however when we fetch any report for these devices we get a blank report/Graph.

What could be the issue? 

Below is the part of configuration on the routers. 

ip flow-cache timeout inactive 60

ip flow-cache timeout active 1

ip flow-export source Loopback1

ip flow-export version 5

ip flow-export destination 10.1.40.70 9996

Interface GigabitEthernet3/15

 ip flow egress

Same configurations has been put in other models of Cisco routers and it is working properly.