Same here with my iPhone 5.
With iOS 9.2.1 I faced random Wi-Fi disconnecting or such situations, that the Wi-Fi icon in status bar is on, but I've still got no Internet connection. When I try to load simple web pages it takes much longer, than usually. And Apple Music is not playing not downloaded tracks at all. The only temporary solution, that helps is simply rebooting the device. But sometimes this issue happens several times per day and it frustrates me a lot.
I've tried resetting the network settings, but that didn't help. Turning off Wi-Fi assist didn't help either. This issue does not seem to depend on a Wi-Fi router as well - it happened when iPhone was connected to the latest Airport Express, MikroTik and TP-Link models.
Also, loosing connection randomly with Apple Watch via bluetooth is another problem. I tried repairing and resetting the Watch, but nothing helped.