I was using a legendary RP boost. Can you say ouch?
Ah, that’s a huge bummer. Happened to me, but I got AFK kicked, despite returning just as the game kicked me. 
Was it Arena, though? Legendary Arena boosts hardly give you anything. :-/
Dang that sucks. I’ve been disconnected a couple times and also a couple game freezes but never while using a boost thank God lol