Z-Wave Groups - Delay After Command

I have set up some Z-Wave lights (8 total) and put them in a Z-Wave group. When I trigger the group to turn them all on it will work with all lights instantly turning on. If I then try to dim, change color or turn off the lights I need to wait 12-15 seconds before I can.

For example, if I turn the z-wave group on then back off, the light turns on then nothing will happen, at all. If I turn it on wait 15 seconds then turn it off the group will instantly turn off.

It is like there is a cool-down period before the group will accept another command? Is there a way to fix this?

I used the z-wave group as it turns on all 8 lights at the exact time, if I use a light group the individual lights do not turn on in unison, they will turn on individually