Leviton Switches without Ground

Does anyone know if Leviton Z-Wave switches will work properly without being grounded? I suspect they would, since my old home does not have ground wires in the outlet or switch boxes, yet all plug-in type modules work fine.

I’m asking since I’m having trouble with two Leviton devices (DZS15 and DZMX1). The paired initially, but are now having problems responding to ST.