How can I try to hold a gym? I can't interact with the players from "my" team and I don't get attack notifications to be able to react. So suddenly my gym switc

How can I try to hold a gym? I can't interact with the players from "my" team and I don't get attack notifications to be able to react. So suddenly my gym switched color which I can actively check after the fact. In good old Ingress I got an attack notification and (remote) recharge or (locally) refill with resonators or emergency switch it using a virus, thus prevent the attack. I reached Level 14 in Go and uninstalled it. Will probably try in a few versions, again. But for now this wasn't much fun.