Sonicwall TZ500 dropping connection from Spectrum modem

This is a strange one. I have a TZ500 with a static IP connected to a Spectrum modem (don'thave the model). It will not stay connected to the internet with DHCP devices attached to it. I can get to the management portal of the Sonicwall from inside the LAN and can do anything but access the outside world. We have 3 IP phones and a copier all with static IPs on the network and the TZ500 will stay online with these connectedand I can even go so far as to connect to the web management console in the copier remotely. However, when we connect a device that gets DHCP from the Sonicwall, that's when the connection drops and the TZ500 is no longer accessible from the outside.

If I disconnect the devices (2 laptops and an access point) from the switch, reboot the router it comes back online. I went so far as to take everything off the network...