Don't you use redundant interfaces??
I'm afraid, no! It's always been Aggregate and redundant is not even an option in mt FGT. Mabe the bigger chassis supports this, but I have seen redundant type in years maybe decades, but it truly sounds like mac-addr layer2 issues.
If you're seeing ALL layer3 address, I would review the switch ports connected to port3 and port4, the switch CONTROLS forwarding not your layey3 device. I would also check that nobody setup a mirror or span port