Ultracite Terror Instant Killing Me?

I've been able to solo the Ultracite Terror in around 3 minutes. Haven't had any issues until tonight.

Three times in a row I did my normal routine; cripple all the plates, kill the tail, use some coffee and burn the eyes.

Then each time right before I kill the snake, BOOM! I'm insta killed. No warning about the snake drawing in a bunch of air, just pop and I'm dead.

Is this a glitch? Has anyone else experienced this?