Failover not working

I have two wans. In failover setup. 

in theory while primary is up, no traffic should be passing through secondary wan. But from graph I see traffic.

There is no rule in FWG to force certain traffic on secondary. 

‘FWG is in dmz of both isp routers. 

not sure 

is failover not working or FWG is capturing some other traffic not passing through FWG. (Such smart home traffic of isp , not visible to us. ) 

Advise requested.