Same issue here. Out of 6 new RUT240's I've received in the past month, only one has working DHCP on the WAN port. 3 came with firmware that isn't even listed on the website as being a real version, but I was able to update them to the latest firmware. Still nothing. Wiped config, factory reset, nadda. There doesn't seem to be a dhcp client installed on the device as far as I can tell.
Static IP configuration works fine, so there's nothing wrong with the port. Just never even attempts a DHCP request.
I've also watched the LAN for a DHCP broadcast, but none is ever sent out. It's like they just forgot the DHCP client in most versions of the firmware for this unit.
I'm a little miffed as I just switched over to Teltonika from Cradlepoint, but now I've got a ton of dead devices and nothing I can deploy to clients.