If you are in a zone, then use a portal to leave, then go back through your portal into that zone, you are invincible. I have tested this many times and it has worked each time.
It isn’t a visual bug, I sat facetanking for minutes against large mobs and never lost health nor died, even though the red damage counters show up.
Very easy to replicate.
I can confirm this. Glad it doesn’t work on monoliths