Aatrox Bloodwell doesn't go off? (Patch 5.13)

I created a custom game to test out Sated Devourer on Aatrox. I fought Lucian under tower comfortably that my Bloodwell would save me should something bad happen. I kill Lucian and turn away as i'm about to die from tower and when im in the clear and one Caitlyn basic away from death of course she shows up and hits me once. This is all still fine as my Bloodwell is still up and so i happily take the hit but... --Bug--

• Bloodwell did not trigger when took lethal damage.