[GAMEPLAY] Blitzcrank has a 100 health shield that doesn't take damage midway through games

Me and my friend have both had experiences that midway through pvp games blitzcrank gains a 100-150 health shield that appears on the champion health bar that does not absorb damage and doesn't go away. We've observed this happening three times, but haven't found anything specific that triggers it.

This has happened with the base blitzcrank skin and I-Blitzcrank, with Eye of the Equinox, Boots of Swiftness, Zeke's Harbinger, and Mikael's, and sheen. (don't know if that helps)