It's often convenient to use verbal shorthand, but you run the risk that some people won't know all of your communication shortcuts. Take the time to make your messages as direct as possible. Don't let frustration shut you off from the employee's signals.
Some workers expect to be perpetually misunderstood by their supervisors.
Your effort to connect with them might be one of the most pleasant and productive surprises of their working lives. If you typically talk to the employee at a particular time of day or use the same kind of feedback each time, change your approach. It might be just what's needed to shake loose whatever's blocking communication. Don't keep your intentions a secret. Let distant workers help you bridge the communication gap.