Anivia Egg Passive Death Glitch

I wish I investigated more, but in the heat of battle.. I am Anivia vs. Swain . My egg passive is active, but when i take critical damage, i die instead of transforming to egg form. Same thing 2 games later vs Ahri . I think its a bug concerning damage over time abilities. Continuing damage into egg form caused instant death. No science, just conjecture. Any word on this occurring elsewhere?

The egg worked fine otherwise throughout the game. Thank you.