This is an extended comment containing some suggestions of things to try and help you diagnose your problem, but I don't claim that any of these will definitely solve your issue:

### Check `defaults` to look for clashing keyboard shortcuts

Your service runs with a different shortcut and inside _Automator_.  So there is possibly a conflicting shortcut that has appeared and is blocking your original.

In _Terminal_ (or other terminal emulator), you can retrieve all the active app-specific keyboard shortcuts:

```sh
defaults find NSUserKeyEquivalents
```

and your service workflow shortcuts:

```sh
defaults find NSServicesStatus 
```

The symbols used to represent modifier keys are:

  - **`@`**: <kbd>⌘</kbd> _`command`_
  - **`$`**: <kbd>⇧</kbd> _`shift`_
  - **`~`**: <kbd>⌥</kbd> _`alt`/`option`_
  - **`^`**: <kbd>⌃</kbd> _`ctrl`_

Thus, <kbd>⌘</kbd>+<kbd>⌥</kbd>+<kbd>⌃</kbd>+<kbd>C</kbd> is symbolised as `@~^c` (the `c` is lowercase).

You can do a general `defaults` search through all the preference files to look for that specific combination of characters:

```sh
defaults find '@~^c'
```

You can also search for matching preferences files:

```sh
grep -iE '@~\^c' ~/Library/Preferences/* /Library/Preferences/* 2>/dev/null
```

which, upon matching, will output something like:

```sh
Binary file /Users/CK/Library/Preferences/com.apple.ServicesMenu.Services.plist matches
```

and then you can target the specific domain to examine its `defaults`:

```sh
defaults read com.apple.ServicesMenu.Services
```

### Third-party Application

There are third-party apps that allow you to see what keyboard shortcuts are being used by which applications on your system.  The one I know of is [**KeyCue**](https://www.ergonis.com/products/keycue/):

<img src="https://www.ergonis.com/images/products/kc/kc_finder-tenaya.png">

<img src="https://www.ergonis.com/images/products/kc/kc_dark.png">

I'm not endorsing the product and have never used it myself, but I believe it would be very useful in finding out if there's interference from another application or from within _Finder_ stopping you from using that shortcut combination.

It's a paid app (€19.99), but has a free evaluation period:

> _All our products are available for evaluation before purchase. As long as you do not have a license key, KeyCue operates in trial mode and occasionally displays a registration reminder instead of the shortcut table._