When troubleshooting wifi issues with the hub, this guide is helpful. https://support.smartthings.com/hc/en-us/articles/205956920-What-do-the-LED-colors-on-the-Hub-mean-
Switching Hub to Wifi or Updating Wifi Credentials
Preparation: What you'll need
Switching your SmartThings hub to wifi can take up to 15 minutes.
SmartThings hub connected to a power outlet and connected to the internet router using the supplied ethernet cord.
Paper clip or similar item (ethernet and power cord come wrapped in a twist tie that can be used).
A mobile device with the SmartThings app installed and logged in using the credentials below.
Soft Reset
Touch Menu
Touch the gear at the top of the menu for Settings
Touch update Wi-Fi information
Select the appropriate hub from the options and then tap
Using the pin (or other small tool) press and hold the red, recessed button on the back of the hub until the LED begins blinking red/green (it should only take a few seconds)
Touch next on the mobile device
Using your mobile device's camera, scan the QR code located on the back of the hub or enter the serial number manually
Select the Landing wifi network
Enter "smoothlanding" as the wifi password and tap connect
Once the hub is connected, tap done. The hub no longer needs to be connected to the router to work. Confirm connection after disconnecting from router.