Switch forwards packets to Fortigates as if there is load balance, but there is no load balance

I have 2 fortigate clusters on my network. One is for sslvpn and the other one is for the internet(rest of the traffic other than sslvpn). They are connected to the internet router via a switch in between. They both have different public IP addresses, however, when i ping sslvpn firewall from outside, packets arrive to both internet and sslvpn firewalls as if there is a load balance (I sniff the trafic using sniffer command). It is very confusing bcs the IP addresses are different and there is no load balance at all. What can be the reason behind? Or do you have any other recommendations for tshoot? Thx in advance 

sslvpn -> 400F (active passive ha)
Internet -> 600E (active passive ha)