Have you checked Preferences, Keyboard, Text (tab) to see if you have any kind of shortcut setup for sc?
Do you perhaps have a utility like Typinator or similarly installed with sc allocated to do something? For example, if I type dual (letter) v together, it will convert text on the clipboard into plain text. I couldn't even type 2 V's together in that sentence without them seemingly oddly disappearing and nothing seeming to happen (sound familiar?).
While I didn't try it, I suspect if I accidentally (or purposely) allocated sc as a Typinator shortcut with nothing in the "replacement" field, I believe it would perfectly replicate what you're experiencing. So maybe you've punched it in as a shortcut in that kind of app without an action and that's what's happening. Typinator sometimes gets locked out by Safari, so it would even make sense that it does as you describe sometimes but not other times.
On a Monterey Mac, I just tried sc in the Safari search bar and it didn't replicate. If this was widespread, it would be much more covered than 1 or 2 instances. For example, Mac users living in South Carolina would have likely crashed into this problem too many times.