you didn’t give the model number but since it’s at least two years old, GE/Jasco switches are notorious for locking up as they start to get older. There’s been a number of threads here and on other Home automation forums about this. The switches will be out of warranty by the time this starts to happen, so technically they aren’t defective, but it is annoying.
The first thing to try is throwing the power at the circuit breaker, not just the airgap switch. This has been known to clear the internal buffer and restart them so they can be contacted via Z wave again.