The phantom disappearance of Wifi connectivity (looks like it's connected, but it's not) is related to bluetooth.
I've confirmed this through a month of testing. When you enable bluetooth, connect a bluetooth device and wifi - eventually both will stop working. The timing varies, but it will happen. The only solid fix is a reboot, although sometime you can turn on/off airplane mode.
I confirmed it's bluetooth by testing various scenarios - if you disable bluetooth and never connect any bluetooth device, you will most likely never have a WiFi issue. There seems to be a problem with the driver for the bluetooth/wireless radio. Hopefully they can fix it in a future update.
The biggest pain in the @$$ is that if you have a fitbit, or an MS band - the bluetooth connection will appear connected but randomly die. So, it makes the band essentially worthless because you cannot count on it staying connected.