@cheapie408 where in your "modem" which doesn't have a public IP.. You mean your gateway, a modem/router combo that you put into bridge mode.. Modems don't get put into bridge mode.
And yeah its possible for them to passthru a different public IP to the client than what it has.. Many of those devices can do passthru, ie bridge mode and also still do nat for devices connected to its other ports, etc.
Have seen this a lot in business deployments of comcast/xfinity.
Rebooting switches wouldn't have anything to do with it - other then the interfaces would cycle if you rebooted the switch, do you have a switch between your isp device and pfsense wan?