Possible Rengar ! Bug

The other day I was playing in a game as Malzahar vs a zed, I got him low so he was playing back, then he starting moving up so I knew rengar was about to gank me, then not even a second later Rengar shows up and kills me

Normally this wouldn't be a problem, but I didn't see an exclamation mark AT ALL until the instant right before he jumped on me and killed me

About 10 minutes later in the game, my sejuani said the same thing, rengar killed her and she was like "wtf no exclamation mark"