As far as your GPS issue, it sometimes happens with certain providers in certain spaces especially during ACTUAL cloudy weather. My best advice is to turn your GPS to worst setting, then turn things to more refined one by one until they're all back to normal. That usually locks me in place at bad gyms for around two or three minutes.
Also, if you're able to enter the lobby but fear you may drift away, turn off your GPS until the raid timer comes up (but do so before the boss is defeated). As long as you don't relobby, you can go as far as you like or drift takes you.
