Automator service works everywhere except when using keyboard shortcut
It is working fine here.

However in my experience most problems using UI sequences are related to the lack of delay for the system to execute the thread. Often it will process the strokes so fast that the actions are not yet finished before automator sends another command, causing overlays and hence ignoring the last action. A simple solution is providing tiny delays between each stroke. 

Also the return input line can be causing issues, because the input is empty and there is no parameters.

I have tested this script successfully:

on run
    tell application "Google Chrome" to activate
    delay 0.1
    tell application "System Events"
        key code 34 using {control down, option down}
        delay 0.1
        key code 15
    end tell
end run