Please read "Table 1 Where to Configure NetFlow Accounting and Which NetFlow Commands to Configure" in this document(link below) to make sure you have netflow configured properly on tunnel interfaces. You probably don't have netflow configured correctly on your Tunnel interface(s)
Do you have the following lines in your config?
ip flow-export source xxxxxxx
ip flow-export version 5
ip flow-export destination x.x.x.x 2055