Keyboard shortcut not working in yosemite

I have reported this bug to apple and it's still not being closed. I will update my answer once it's closed.

Till then you can add this shortcuts under all applications(instead of preview) then it will work.

I don't know why this isn't working either, but I ran into it with Mavericks too.

I've tried both "…" (proper ellipses) and "..." (three .) and neither of them work.

So I made a Keyboard Maestro macro for it instead:

The key here is that the "Group" (labeled "1") is set up to only be active in Preview.app.

Then the macro (labeled 2) is where we explain what we want to have happen.

The "Trigger" (3) in this case is the same keyboard shortcut (aka "hot key") ⌘ ⇧ Z but could be anything

Then the action is to trigger the menu item Tools ---> Adjust Size...

(The "Stop macro is menu cannot be selected" might seem superfluous since there are no more actions after this one, however, if that happens, Keyboard Maestro will show an error to the user, which can be helpful. Otherwise it just silently fails.)

You can download my Keyboard Maestro macro here. Unzip it, double click on it to import it into Keyboard Maestro, and it will create the "Preview only" group and add the macro to it.

I still don't know why the official Keyboard Shortcut doesn't work in Preview.app, but an added bonus of using Keyboard Maestro is that since it can sync (using iCloud Drive or Dropbox), you can have it on all of your Macs. Keyboard Shortcuts added to the OS X System Preferences don't sync. Yet another reason I like Keyboard Maestro.