It is because we made the DHCP timout larger in the Mach3 plugin, because we got some report of slow routers and networks where the DHCP address gathering routine failed, because the router responded too slow.
Now the problem is why you can't put the UCCNC firmware back is because the UCCNC API side times out too fast.
What you can do:
1.) Connect the UC300ETH directly to the PC and disable the DHCP for the firmware update. After that you can connect it back to the network.
2.) Disable the DHCP in the router and use fix IP.
3.) Wait for the next UCCNC release where the DHCP timeout will be the same is what it is in the Mach3 plugin.