I'm having the same problem. It tells me I've left my fireteam even when I'm out doing a patrol by myself and not in a fireteam. It happens in patrols, missions, pvp, strikes, raids, and even just in the social spaces like the Tower and Reef. I've tried uninstalling and reinstalling but that doesn't seem to have worked. I'm playing on Xbox One. Also experienced the problem of being told my "trial period" has expired and that I have to purchase the game. I've already purchased the game and all of the DLC and expansion. Anyone able to help? Maybe Bungie since it's their game thats so ridiculously broken?