After the Nexus blitz URF event, i was permanently missing about 300 hp on Rengar. It was showing I could heal the missing 300 HP with my W, but that didnt work. If i died i was still missing 300 HP, this was not just a visual bug either, i was actually missing 300 HP all game long after the URF event, and it was even more annoying because i couldnt tell how much HP my W was actually going to heal me.
If i had 1500 HP, i actually had 1200 HP. I have played quite few games with Rengar, but this bug only happens after the URF event with Rengar.