disorder in Notification Center

I don't know why, always I re-start a session on my MacBook (late 2010) the Widgets on the Notification center gets disordered, like a mess, I don't want to re-organize them every time I need a tool. Someone can help me?

MacBook 13-INCH late 2010

OS X El Capitan 10.11.5 (ONLY S.O. / partition)

no-bootcamp