You may want to try doing a Z-Wave repair. Also it helps to have a few mains powered Z-Wave Plus devices around to help the mesh and connectivity.
Some 2GiG thermostat models have the ability to act as repeaters for the mesh but require them to be paired with the C-Wire connected. You can find more details about it here: [RELEASE] Enhanced Z-Wave Thermostat Device Handler with Z-Wave Plus
Note that most “lights” do not act as repeaters but “switches” should, in which case doing a Z-Wave repair can fix most issues.