Enemy HP keeps resetting in Converged City

In the Converged City, there is a group of Venatori enemies close to a gate with a red barrier. Their HP keeps increasing back to full. What are they doing? How do you block it? It makes them literal punching bags until they get staggered enough to try and kill them in one or a few hits.

It seems like a bug since the game has not once mentioned that this is possible, and nothing in the environment seems to be helping them. Each enemy is both attacking and resetting its HP simultaneously and continually.

If it is not a bug, then it should be more obvious how to stop it other than spamming attacks to stagger the enemies.