I'm playing Magic Arena after quite a long time away from Magic. I still remember how to play but there's something that's keeping me confused about the priority system.
When I'm passing the turn, eventually the opponent plays an instant speed spell before his turn, and the game does not allow me to respond to it. I didn't remember this rule but still OK (although that make instants and permanent spells with flash much more powerful than I thought they were).
But in my last game I just played an enchantment with flash at the end of my opponent's turn, hoping that my opponent could not answer to it with a counter spell, but they were able to respond and indeed countered it.
I searched for rules of end-of-turn casting and I think that it's just a glitch of the game (it's still on beta and there's some of them), but I'm not sure. Any help will be appreciated.