t14 Constrictor just is nearly immortal

Attempting this guardian, and every time I start to damage him, he just heals to full. I seem to be rolling through lots of stuff no problem on my TR Raider, and this is really frustrating. I'm looking at all his abilities, and nothing shows leaching or recovery, so I'm pretty perplexed.

Just re-rolling the map now, I'm not going to sit here and just attack while he heals to full, so pretty big waste for me :(

Any record of what the map's mods were? Or if the Maven was watching?

If Maven is witnessing she does heals, the line says something about vitality which will give him a surge of health.
If your damage is quite low and say map mods had ~70% increased life with monster chaos res he might be able to out heal your damage.