Why was my full node knocked off the network last night?
As Nate Eldredge said, the block that you received is a Bitcoin Cash block which is invalid to Bitcoin Core. Because of this, your node banned the Bitcoin Cash node that sent you the block. However, it seems like the way that you have your node set up is that the gateway is acting as a proxy instead of passing through the connections. Thus Bitcoin Core thinks the connection came from your gateway instead of from where it actually came from. When your node banned the Bitcoin ABC node, it banned your gateway as it thought that was the bad node. This had the effect of then banning everything connected to you because they all connect through that gateway and the gateway was banned. The connections are back today because the ban is only for 24 hours.

I highly suggest that you make sure that the connections are properly being passed through so that this does not happen in the future. To ensure that they are passed through, if you use getpeerinfo (or the Peers tab of the Debug Window if you are using the GUI) and look at the IP addresses of all of the nodes you are connected to, they should not be the IP address of your gateway.