Lissandra ult doesnt make her Invincible? [GAMEPLAY]

Hello Riot,

I think Ive uncovered a bug within Lissandra's ult. i have the video to show but Im not quite sure how to post it here. basically upon entry of the ult which states once activated on Lissandra herself she becomes untargetable and invincible but she still dying in the middle of her ult. Now in my video i popped the ult before all the slowing effect spanned out so i thought maybe she has to fully be in the ult to be invincible? If im able to post the video id like you guys to decide. Please get back to me as soon as possible. Illl try and upload screenshots.

I get cut off so in a ditch effort I ult to do as much dmg possible.
in the middle of me ulting i get snared by a maokai and damaged by a nid spear and a zed w (i believe)
watching the cocoon take full form a jhin 4th shot hits me directly and I die. slowing effect animation has gone completely through at this point

P.S I have the video of the situation but it looks like I can only email via zip drive. Would that suffice? Thank you,

Eab245