Number of Endpoints in a specific group keeps varying

Hi All

I have installed few systems with the symantec and it was reflecting in the console under the group which I had created.Today when I checked under the same group I saw that the number of systems has come down from 152 to 116 and few minutes later it became 119. I have checked if it is displaying just online systems but no, it is also displaying offline systems. Can anyone help me understand why this is happening? Thanks in advance.