LAG connection setup

Hi,

would like to seek for your advise for the current setup attached, basically we have another firewall on the right side of the diagram that connect to L2 switch, and on the FW side the port is configured as LAG while on the switch is under port-channel, but take note the switches are two separate standalone (not on stack).

every time we connect the cable c3 and c4 the network is disrupted, is it because the aggregated ID is different from the firewall perspective?

I always see this setup as common, but they always use stack switches.