iPhone 7 Plus have two WiFi MAC address I know some devices have two WiFi MACs (one for 2.4GHz and one for 5GHz).

In some network monitoring like Fing.app my iPhone is displayed twice with the same IP but totally different MAC.

PS: but "both" devices have a different bonjour name.

Any more info on this?
Since iOS 8 the system generates a randomized MAC address. I thought it was every time you connect to a different network and on every restart.

So you have technically 2 separate networks which means you have also 2 different MAC addresses.