Cheated out of IP

So yesterday i was playing a game with my friend and after it was finished I was like "oh cool I have a straight 6k IP". Fast-forward to today, we finished a match and i got my first win of the day bonus which was 150(like usual) and I earned 58 from the match itself, plus 18 because it was a match game. I only have 6179. I'm missing 47 IP and I haven't bought anything. What happened? I know IP takes a while to build up anyway because Riot wants us to spend RP on everything but now that I finally have some to buy a champ I've noticed that some of it has gone missing. Whats going on?

Inb4 you just want free IP

I just want this solved so it doesn't happen again