It turns out Android M thinks your Android Wear app needs to take a nap every once in a while.
It should be no surprise to anyone out there that the Android M Developer Preview is not 100% ready for public consumption. We're not expecting a Nexus running the finished version of this OS until the fall, but that doesn't stop folks from giving the preview a quick flash and checking things out. In doing so, a few folks — including our TWiT friend Jason Howell — noticed Android Wear didn't always behave as expected when connected to the preview.
It turns out this has more to do with Android M's new App standby functionality and the Wear app not being ready for M than anything else. It also means there's an easy way to stop this from being a problem.
The App standby function of Android M sets apps up for auto-shutdown when the system feels there's no need for the app to continue running in the background. When you consider Android Wear is specifically designed to constantly run in the background so you can sync with your phone, it's not hard to see where problems would arise. To fix this, hop into the Battery Optimizations section of the battery manager in Android M and set the Android Wear app to ignore optimizations. This will keep the watch connected to your phone, and let you get back to totally not using a Developer Preview as your daily driver.