Client Bug
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It's simple, and I think almost everyone had this problem before. Client bug, the client just stop working. Doesn't care if you are in Shop or in queue or CHAMP SELECT! For me this little thing was not a big problem, I just waited for the leavebuster or smth to past if I was in champ select. But I lost my promos and I didn't lost it because of my fault or gameplay but because of client problem. That pissed me off! damn... 
*I need to say that is not because of my computer, I have five years of League of Legends and never had this problem before the last updates.