Can't comment selection

Question

Sometimes, it seems I can\'t comment my code with the usual shortcut (command + /) under Xcode 8 Beta 4. The option is disabled in the menu (screen

Answer 1

This bug also happens on Xcode 8.2.1 (8C1002) of macOS 10.12.3 (16D32). And there is another Xcode 7.3, which is fine, also installed on my machine.

I find two solutions:
1. Type sudo /usr/libexec/xpccachectl in Terminal, then reboot.
2. rename the Xcode 8.2.1 to Xcode8,restart Xcode8, now it works!