Strange issue ...

have resettled the router now several times - always ending at the same issue:

After the reset the setup wizard is working fine, router adminpage is accessible without issues. Standard config. But - as soon I connect the ISP modem (I see that the router get's the IP on the wan2 interface immediately) I can't access the admin page anymore. wLan is telling me "no internet connection"

Funny enough - as I also run a Omada controller (OC200) and this is the only device capable to access the internet - and is also reachable from external. At the OC200 Interface I see all devices - also the ER706W - but I'm also not able to adopt it ... 

There are NO vLan (except vlan1 by default) configured

There are no FW rules

The only thing I found was that if mesh is turned on it can cause issues - so mesh is disabled now - but no luck so far.

Any Idea what's going on here?

Regards