I had the same issue here, not sure of you have the same siren:
For me, the panel is within 15 ft of the siren, in the other room, but z-wave can be flakey no matter the distance. I rarely get alarms, so not sure if this is a one off. If it happens again, I was hoping to try the siren test again so that is send signals to the siren to turn on and off. But, if it happens again, than probably another issue at hand.