I tracked the problem down and it's the router

I had some other machines to test and a Windows/Linux PC does the same (see below) as does a PS3.
OK, not exactly the same but both machines do NOT have working internet access on the first boot although the router has a flatrate and is always hooked to the internet.
On the PC: The NAS is not available before some seconds after complete bootup (as is on the Amiga).
This behaviour is "new", it didn't do it "before"
On the PS3: I get a network error on every boot, but it will still access the net and work fine after some seconds.
It seems my router (Fritz!Box 7390) lags on the IPs?
All this testing tells me (i hope) that not a third-party program is crashing/asserting but the AddNetInterface program trying to access the net in the first go or checking if there is internet or whatever it does on the first start.
The main problem is NOT with AmigaOS!!!
Still it would be nice if it wouldn't just assert but rather bring up a window...
I'll check related forums for help on the main problem.
Thanks so far