This video is of the second time it’s happened. Included in the description of the video is the lastepochtools build planner with the exact character in question imported, I will also link it here: Paladin, Level 69 (LE Beta 0.8.3c) - Last Epoch Build Planner
When channeling Warpath on my Paladin, I use it to trigger a large number of skills, including:
Smite, from Warpath tree
Path of Fire, from Warpath tree
Divine Bolt, from Paladin tree
Magma Shards, from Volcanus unique flamberge
Flame Burst, from Holy Aura tree
On two occasions I have had a large black circle like the one in the video appear around my character, and I become completely immune to damage and unable to deal any damage. This persists through changing areas, gear, etc, and will only end when logging out and back in. Notably I am still able to hit and be hit, trigger my on-hit abilities, be poisoned etc, I just take no damage and deal no damage.