Arduino atmega2560 with wiznet850

I have two costume boards based on Arduino mega2560 with wiznet850 ethernet module to send UDP packet over ethernet. one of them has atmega2560 16u-TW and the other one has atmega2560 16u-TH .

I checked the hardware connection for both boards and everything is working.

the issuse is that the first board (with atmega2560 16u-TW) is just working fine, meaning it takes an ip and i can ping it from my pc locally. however; the one with (atmega2560 16u-TH)can not take an ip ( it shows me that ip is and sometimes

doese anyone faced the same problem on know why this happens?

is the MAC address different?

Did you try swapping Ethernet modules?

yes I am sure they are different

yes, i did swap the modules and i get the same issue

do you think (TH) and (TW) would be the reason for this issue?