This is not about glow squid becoming dark after getting hit.

Glow squid remains dark even if there is a light source block next to it. There wouldn't be anything wrong with that, since when near surface or on land, their look doesn't change at all after getting hit, even though tag is updated.

In short: block light sources do not affect glow squid at all

Glow squid seen on second screenshot has been hit. I added it, to compare how it should look like near block light sources