The A4 has 2 MAC address. One for CDMA and one for LTE. I know this because I use it in my office network. All the MAC address has to be whitelisted. The MAC address on the label is only one of it. The other MAC address is either 1 up or 1 down. I don't remember.
So for Airave 4 to work, your modem need to be able to provide 2 IP address to A4. If you plug it directly into a cable modem, it is very likely your ISP doesn't want to supply 2 IP address. So, try to put a router in front of it.