Any news on this? In the meantime, there are several threads about this, like this one …
Web → Internet → Cable → (button Modify →) Protocol: This thread here describes ‘DHCP’. ‘PPPoE’ is affected, too …
It is OK, to have a mode ‘relay’. Other router vendors call this ‘pass-trough’. However, that is should not be the default. And ‘native’ – on the GL.iNet side – has to be ‘server’ on the OpenWrt side.