EC25: udhcpc does not get a lease


I’m running an LTE module (EC25EFAR06A11M4G) on Linux (Ubuntu 16.04).
My wwan0 interface does not receive a lease via DHCP (udhcpc ver. 1.22.1). I have set the ip-raw mode and there is no other dhcp client running on the system.

What could be the reason?