I have experienced multiple times while questing in a group. We all are on a 4 person mount, if that helps.
We finish a battle and then it used to be many seconds of just being immune to engaging into a battle again if idle.
Although what annoys be sometimes is that I also watch videos when questing, so I can get distracted when it's the final round. Because of that distraction and I'm the driver of the mount, they get pulled into the battle we just finished. Takes only 3 seconds tops if the mobs are walking right where our battle was. Because of this if I had to go do something besides the game, they would be instantly put back into battle. I was just battling in Khrysalis in the Ruined Alchkazar and finished a battle and instatnly put back in. It's so quick, sometimes I can't even respond when my hands are off the keyboard quick enough and at least one player still goes in.
Is there a way to grant more time back, it's only a few seconds at best for us. I feel if idle, you stay immune, like it was before. If you move, of course you have a small timer before you can join a fight again. For us we don't have an immune time, we have to get out asap or we will be back in one.
So the many players who are farming should all have to wait because you are watching videos elsewhere? I see a quicker battle time as a feature not a problem. I don't think the game should be designed around people who aren't even willing to pay attention to it. Stop watching videos or let someone more attentive drive a mount?