The problem is that with both WAN and WWAN on the same subnet the S1 can receive packets on the WWAN interface but replies on the WAN interface so wifi access only work with the Ethernet cable plugged in.

Quick fix is to connect via cable and move the WAN interface to a different subnet

(e.g. IP - 192.168.2.42
Subnet - 255.255.255.0
Gateway - 192.168.2.1)

If it doesn't work you will need to give your PC a static IP address on the 192.168.2.0/24 subnet to get back into the S1 to fix things.