The problem is: When I switch it to fixed IP I will not be able to notice all devices if I swap the main router, especially when I do that from remote. It could be that the main router wants to...

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You might get an answer if we could read your post and didn't have to play detective..

What do you mean by cascade? I use a TL-R470 with one DSL modem as WAN1 with PPoE and two other DSL routers as WAN2 and WAN3 with DHCP. In a certain way that's a cascade of routers. If you meant...

That might be one guess. How about fixing the bug? If the accesspoint can't work properly in DHCP mode, DHCP mode should not be sold. I even suspect that this would not solve the problem. It's lke...

Ah sorry - I overlooked that. Yes, then it is an issue...