After reaching out to Nest customer service via live chat, I was able to solve my own issue. If you don’t have some devices showing up in SmartThings that should, it’s most likely a cache issue on your phone. I was able to resolve the issue by restarting my Thermostat (by pressing it down for 10 seconds) and reinstalling the following apps: SmartThings, Nest, Google Home. Once I re-logged into each app and re-synced Nest with SmartThings, all of my devices appeared as expected. Hope this helps other people! 