I have several HS200's around my house and every few days when i send voice commands, or try and access them through the alexa app, the device is unavailable or says its unreachable. It's not always the same switches either. I have some of them setup in groups, and I'll tell alexa to turn off a group, and 1 of the lights will stay on or will take 15+ seconds before it turns off. The signal on all of them is between -40 db and -55 db.  

What can i do to prevent these switches from ebing unreachable?

Thanks