My rating on jungle gin goes down when I am not playing, why?

[dgee44]

@EA_Arrenai When the new hd jungle gin came on my rating was 1001, dropped to 981, back to 1001, down to 968. Why is if fluctuating so much?

[Jankelly2003]

@EA_Arrenai This is a common problem and happens to me most days. Sometimes only one or two points but today my score dropped by 35 points without me playing a single game.