[GAMEPLAY] Demon Vi is so powerful she can kill Demonblade Tryndamere under his ult

I tried to fight a fed Demon Vi with my ult up as Demonblade Tryndamere. Everything went off as the ult should've, then she just punches me and I died while under the ult. She had red buff on her as well.

I have no clear idea how to reproduce this bug, but all I know is she slapped me with her new fists, powered by red buff, all while I ulted.

I don't know how frequent the bug is, as it was my first time encountering it, but the video can probably tell a better story.