I have the same issue but it's only shortly after my phone screen has locked. It will disconnect from my garmin watch within a couple of minutes of locking. I've reset the cache, reset network, done a factory reset on my watch. Gone through every setting I can find to ensure apps are running in the background etc and am totally over it. There's no point having a smart watch if it won't connect to my phone.
I have left wifi off and found absolutely no difference. My watch will still disconnect from my phone within a couple of minutes. I thought my watch was the problem but after reading this thread it seems the phone is. Really disappointed as I have only had it a month
