Once again the stuck at 33% thing is happening to me. I updated league yesterday and played with no problem now I have to wait hours until it stop scanning files. Did Riot say anything about this or is there a confirmed way to stop this without waiting hours?
I have this problem too...
So I think I may have the fix if you're on a mac, and basically what you need to do is open up Activity Monitor (easy find in Spotlight), then find UserKernel. Then, quit UserKernel (double-click, click quit, enter, done.), and wait a bit. I had to wait maybe 5-10 minutes whereas in previous patches it was closer to 30 seconds to a minute. If this doesn't work, or if you're not on mac, sorry.
Riot has a thread on this over in the Help & Support forum, here -> http://boards.na.leagueoflegends.com/en/c/help-support/zPUA7Zyg-new-having-issues-patching-56-click-here
Alternatively, you should try repairing your client. (Also this is the wrong forum for this problem, try the Help & Support forum)
