After the initial wave of hype over the new raid battles and the new gym system, I’ve been able to find new things about gyms.
For one, I’ve noticed that gyms have been really buggy when you try and collect the pokestop. The camera randomly jumps back down after initially showing the pokestop. It’s strange. You cannot place multiple of the same pokemon in the same gym at the same time (e.g. if I put Snorlax in the gym, no one else can put Snorlax in the gym unless I get kicked out). The maximum number of defenders in a gym is 6, and there is no more “gym level up system,” which means you cannot level up your gym to level 10, which means you can get rid of all those pokemon that you’ve been keeping for leveling up gyms.