https://bugs.winehq.org/show_bug.cgi?id=45145
--- Comment #6 from Michele Renosto composizion3@hotmail.com --- (In reply to blorby from comment #4)
It doesn't prove that's the same bug, but it does look a lot similar.
I think it really is the same bug, I compiled libX11 with the CrossOver's patches provided in that thread and now LeagueClients.exe starts successfully every time.
https://bugs.winehq.org/show_bug.cgi?id=35041#c38