I have one of those chinese "RTL960x based xPON ONU Stic" SFP module which works fine in my old MikroTik router, but my new TP-Link ER7206 seems to be unable to connect to it.

The SFP lamp lights up for a few seconds before it goes out, then the process repeats forever. A new entry saying something like "Succesfully released adress on sfp interface 0.0.0.0" is added to the syslog each time.

This gpon module takes a long time to initialize, at least a few minutes, is it possible that the 7206 times out and resets the module before it have had a chance to come online at all?

The gpon module will not come online at all if no fiber link is present, and it will wait for the fiber link to be ready and an IP adress assigned before it will present itself to the host (router or switch).

This is no problem for the MikroTik router, but the 7206 seems to be unable to handle this.

All the GPON related settings is stored in the sfp module itself, not the router. The router only sees it as an ethernet interface, thus the gpon module will establish a fiber link regardless of the router being correctly configured or not.

It also presents a management interface on 192.168.1.1, in addition to the WAN IP, and a third unrelated IP which is probably the ISPs management network.

The stick is configured to present each network range as separate vlans, but no vlans has been configured in the MikroTik router, it just works somehow.

Nothing works on the 7206 though, as mentioned. The sfp light goes on and off every 10 seconds or so, and that's it. No IP, no link, nothing.