Question: XCode 6 Beta 5 and autocomplete stopped working. I thought problem in Beta 5 but I've reinstall to Beta 4 and it's still not work but it did before. I check preferences for "suggests" and I tried to delete Derived Data but it doesn't help

Answer: 
Check if the .m file has been checked in "Target Membership"
For me it was because it was a new problem since upgrading my version of Xcode. After downloading the documentation again, everything worked fine.