@jandico 

Suggest that you can compare and check if these three MACs are the MACs of your clients.

Because under certain circumstances, for example when it is some clients connected to the SSID of the EAP, but at this time the EAP is in a state where it has just been powered up and has not yet been assigned an IP address. The router will assume that these clients are connected to the gateway.

Also, are the three MAC addresses always displayed, or do they disappear after a while?
Under what circumstances will they disappear? Reboot or reconnect?

Is this an issue you can reproduce consistently? Maybe it's just an occasional problem, as I've never had this happen with my device.

Dear @jandico,

jandico wrote

At some point 3 new tp-link mac addresses appear (no new devices added) Two Mac addresses do have an identical IP address! (see screenshot attached pdf page 1).

I noticed these new mac addresses for the first time some day's after upgrading the two EAP615 devices but I can not identify any relation with these EAP615 devices.....

Especially in the user IP network and IOT network I do regularly check for unknown addresses and i did not add any TP-link devices (all TP-link devices do have a mac bound IP address in our setup)

I'm a bit interested in the issue you posted. Hope it's not too late to reply to your thread.

Was your concern finally resolved? Did you figure out what those 3 devices are?

Did you upgrade the router firmware before the issue start to occur?

What's the current firmware version of your ER7206 router?

Dear @jandico,

jandico wrote

Still no clue where the MAC addresses belong to. I expected the forgotten TP-link extender, it was active but with different MAC addresses.

There are still two similar MAC addresses suggesting direct attached (wired) to the router and using a WIFI identified IP address (original 3).

Thank you for coming back with the updated information.

I can confirm that the MAC addresses that start with 84-16-F9 belongs to TP-Link, but those start with 86-16-F9 or 88-16-F9 doesn't (their vendor cannot be found, I guess they are random MAC addresses).

If you want to check what device it is, perhaps you may try blocking it from the Omada clients list and check which client in your network will lose the connection. And you can unblock the client under Insight -> Known Clients -> Blocked.