[Gameplay] In game Messaging Bug

When I am in the league client (not in game yet), i can message my friend perfectly fine. Once I get in game though, when we do the private messaging (/msg or /w), i can see if he private messages me, but when i do /msg or /r to him to reply, he does not see my private messages. This only happens with one certain friend. I am hoping there is some kind of fix for this. Thanks!