I think the Nest integration is calling so many times the Nest Cloud APIs that the calls end-up to be blocked so even the Google Android Official Nest App is freezing and refuse to connect.
I asked Google to investigate and they replied the following:
This is Kevin again from Nest Senior Support.
The Samsung Smart Things is not supposed to be connected to the nest products. We do not list them as a Work with Nest and Samsung also clearly state on their website that Nest Labs have not been certified. Therefore, the best thing for you to do is use the Google Home only. I appreciate the concern and also for bringing an interesting question. Since the solution is clear, there is not any assistance required from my part, I’m closing this case.
Was great assisting you! Happy Holidays!
If you’d like to check out additional resources, feel free to visit nest.com/support. Or if you need more help with this case, visit nest.com/help. When you contact us, refer to case number 06785491 .
You may want to post in the NST Manager thread. That way, the developers will see your post and give you a response. Two questions, is your NST Manager up-to-date and have you created any automations that my be triggering the rate limits imposed by Nest.
I use NST Manager with 1 thermostat, 5 protects, 6 cams and a hello and everything works for me.