Arduino Ethernet Shield only works on reset

Ethernet Shield only initializes after a reset

From the start: I don't want an immediate solution, I just ask if someone has ever had the following effect!

I have been running an application on an Arduino Mega with Ethernetshield for 4 years and no problems with it.

Now I have recreated the whole thing with another Mega and a shield of the same construction in order to implement extensions and leave the "productive system" alone for the time being.

Now the whole thing has the following effect: Immediately after switching on, I can't get a connection to the Mega. You can also see that in the LED gallery on the shield, which by far does not make the light organ that I am used to in normal operation. One press of reset and it works as it should. I also swapped the shield for verification with the one on the production system. The problem moves with you!

Is there something like an "AdapterReset" in the Ethernet LIB in addition to the Ethernet.begin.

After the reset, this shield also runs stably. At startup I have already built in long delays up to the Ethernet.begin. But that is of no use either. Maybe I could add a break between Ethernet.begin and Server.start and UDP.start.

I have already tried this software with a compatible board (i.e. no shields) and they work too. (There is also a version for this Billicchip where everything is done in SW - I just don't come up with the name (oh yes ENC with UIPEthernet.h) this also works perfectly.