As the title says, I’ve had the same hub STH-ETH-250 for years running on the same Palo Alto firewall. Yesterday, the hub went offline but I still have internet on the rest of the devices (computers, iOS, xbox, Ring, Lutron, etc etc). I can see the hub is sending traffic for DNS, AWS, cloundfront in my firewall logs AND I can control devices like my Lutron lights (has a separate hub) via the smartthings app. All of my zwave/zigbee devices show offline in addition to the ST hub offline. Support was not helpful. Any ideas?
Have you attempted a soft reset?
soft factory reset by following these directions:
- Disconnect the power cable from the Hub
- Using a pin or a small tool, hold down the reset button on the back of the Hub
- While continuing to hold down the reset button, replace the power cable
- When the LED on the front starts flashing yellow, release the button
March 18th…oops! I accidentally edited this post… nothing new in this thread 
sorry!