Nest thermostats. They were an endless source of frustration for me.
The recent iterations are just frustrating. The apps are laggy. It’s always prompting me to join an energy savings program no matter how many times I say no. We had to disable the home/away detection because it went from working well to thinking we were away 5 times per day.
Nest stands as my example of a product that went from great to terrible through complete mismanagement and customer neglect.