Hey there! @Rhysknight Welcome to the Community! 
Do you happen to have the model code for the Series 7 TV that the symptoms occur on? Have you tried ensuring that the devices are synced by the “Ok Google, Sync Devices” command?
Have you already tried factory resetting the TV and then re-adding and relinking to Smart Things and Google Home?
Certain Samsung devices/appliances may not work with the Google integration and product features vary by model.
Additionally, there is a topic similar to the symptoms you are experiencing that may include additional steps for you to try: Samsung TV showing offline in ST when TV powered off - Google Home
I hope this message finds you well!
^SamsungZell