Cho Gath ingame bug

Hi, i have been playing Cho Gath as a support today (i know its not his role) but when i used my ult on a champion and it definitely killed him i didnt get feast stacks. i only got feast stacks by ulting minions but it always only gave 100 health eventhough my ult was lvl 3 and i normally get way more health from it . Hope you can fix it , have a nice day