so you downloaded M5Burner correct? and it opens ok?
what exact model of M5Stick you have - you need to choose correct firmware version.
is your M5Stick com port detected in M5Burner when usb is plugged in to M5Stick?
@felmue Thanks for your reply.
Meanwhile I confirmed being powered by POE has no effect. The problem is the interface never gets an address from the DHCP server.
With a fixed address, everything is fine.
Did you try any other Ethernet lib?