First of all I suggest you check that it is screwed on firmly. There is a small plastic screwdriver that comes with the CV1 for the purpose. If that fails, try removing the earpiece completely and make sure the electrical contacts are clean. You can also try swapping the two earpieces over to find out if it is the actual earpiece that has failed.
Well, you were right, right as I was writing my reply to this, the left earpiece snapped right off.