This one I really hate.
It's bad enough that the play balance is so unpredictable that the only way to beat some green and yellow (and sometimes even GRAY!!!) MOBs is to fight the MOB near the mission exit so that you can zone out, use a treatment, then zone in and fight some more.
But what REALLY irks my goat (to coin a new phrase) is when I've got a MOB down to 1/4 health, but I'm nearly dead, so I zone out.
The MOB casts a root nano on me, and it doesn't take effect until I'm OUT of the mission area. Then I have to stand there for 1-2 minutes waiting for it to expire. I can use maybe 3-4 first aid kits in that time, which doesn't heal me to full. But naturally, when I zone back in, the MOB is back to full health, and I have to start that fight all over again. And there's always a good chance I'll get stuck in a root when I get the MOB back to 1/4 again anyway.
If there's a workaround to this, or any way to cancel the root nano, someone please let me know!