Cannot maximize a window by simply clicking on the Photoshop CC app icon My OS is Yosemite and I work in CC apps daily.
I minimize several ways (clicking on the minimize button in the window, command + M, etc.) but I used to be able to just go down to the Photoshop app icon in my dock, simply click once and all my windows within would maximize.
Please note: I'm not trying to zoom.
Currently I have to go to the icon, click and hold then highlight "Show all Windows" in order for the windows to maximize again.
Does anyone know if there is a system fix? I prefer NOT having to add a source app. Thanks
I know you specifically asked for a system fix, but I'm going to suggest an alternative.  I can understand your frustration with the issue as I've worked with CS apps too.

With option-clicking ( ⌥ + left click ) the program icon in the dock, you toggle the entire app's windows on or off.  It leaves the current state of all open windows and their current position/size.

The click-and-hold method you're using would seem frustrating.  You can get to that quicker by just right-clicking the icon (or in case of a trackpad, 2-finger click), or you could just use the hotkey control + down ( ⌃↓ ).

To be clear, the command + M combo you're using will minimize just whatever window is focused, and the trick I mentioned earlier will not restore it - you will still have to get that back via either the Window menu or the other methods we've discussed.

Also you aren't referring to actually maximizing windows, but rather restoring them I believe.  Maximizing can occur on windows in Yosemite by option-clicking the '+' "full screen" button on a window.  There should also be a shortcut somewhere.