I've worked my paladin up to level 12, but Harbored by light, the shield enhancement that makes enemies take 5d4 when attacking you while you're actively shield blocking doesn't seem to happen all the time.

When I block, I see a white energy gather in my shield arm, and a buff appears at the top of my screen, but enemies don't take the light damage except once every few hits.

Is that how it functions? I just tested it out in Frame work, getting a bunch of minotaurs to attack me, I'd see my shield flash maybe a few times in the middle of a mosh pit, and I'd see light damage indicators maybe... once every few hits.