Fortigate Same Mac Address

I have 2 firewalls, lan and wan. there is also 1 cisco backbone in between. my problem is this: when I make 802.3ad from 1g 2 fiber ports of the firewall, the connection between 2 firewalls is provided. However, when I do 802.3ad with 10g, there is no connection between the two firewalls. The part I pay attention to is this. When I make 802.3ad in 1g connection, the mac address is different in 2 ports. However, when I do 802.3a with 10g, the virtual mac address on 2 ports is the same and only one device appears in the mac address table of the backbone. what is the reason for this?