The 169.254.x.x is the Auto IP address that was recently added to TinyCLR (APIPA (AutoIP))
If it can’t get an address from the DHCP server it will self-assign an address in the 169.254.x.x range.
So it seems it is not getting an address from the DHCP server for some reason. Can you use a fix IP address and see if you can ping the device from a PC?