syncdefaultsd causing a lot of Traffic

Hi!

With "Little Snitch" i´ve noticed, that syncdefaultsd sometimes is causing a lot of traffic.

"Letzte Aktivität" is "last actitity" and sometimes it´s 0 Seconds for Hours.

It´s sending and loading and i have no idea what.

If i´m rebooting the Mac at this Point syncdefaultsd isn´t causing traffic anymore. sometimes for hours, sometimes for days.

i have a traffic based Internet-Connecting with only 10GB (LTE) and it´s a vexation that my Macs are burning up a lot of this.

What´s wrong here and what can i doo?