Well contrary to my expertness than it's something that could be beyond just League itself doing it like oh I don't know memory issues, Java, Adobe Air which sucks, etc etc etc. If it's still doing it after reinstalling League than it's highly likely that it's not League itself but something on your system that's causing issues in relation to League. So far you're the only 1 to ahve posted about this issue so either that means it's something entirely new related to League or it's something entirely due to some issue with your system.
If you're running Windows 10 preview that's your biggest culprit since 10 currently has major issues running League. If you're running 8.1 like I am then your Windows updates are a likely culprit since they seem to be screwy lately.