Hopefully this helps someone. We were away for a week and noticed a few weird things happening in SmartThings, some devices that are always off when in Away Mode were on. Using the device history I was able to see that it was showing that someone was present in our home, the clue was that it was occurring early in the morning and close to every 24 hours. I traced it back to my Google Display rebooting everyday (which is normal), but upon a reboot the display registers a Touch Control event, logically registering someone is present, triggering a routine (turning on a virtual switch), …
So now one less thing for google to do. I had noticed this before but put it down to being in the Beta group and I never bothered to track it down, and of course it is a none issue when we are home.
Good detective work! 
How do you have your device reboot? Do you have it on a power switch or is there some way for it to schedule a reboot on its own? I know you can do it from the Home app, but it requires interaction in the app.
My display has always rebooted itself automatically every day, mostly very early in the morning. I will look thorough the settings, but don’t believe I have ever seen a setting to turn it on/off/.
It appears to be a common/known issue.
We have 2 displays, but neither are used for sleep sounds (we use a Nest Audio), so not sure I would notice. I looked in my activity and don’t see anything like that, but would be kind of nice of if it was an option as I find the displays and speakers just get kind of wonky over time and need a reboot.
We don’t have the hubs/speakers trigger home/away, we just use our phones. . . . but they are all in separate homes with virtual switches back to ST (so we can do different things when different people are home) and none of those homes have any hubs. I wonder if it’s the hub/speaker presence sensing that causes it to reboot.