Hi Jan, there was an empty Order issue introduced in the 2.1.9 urgent release which has been sorted in the 2.1.10 release that went out this afternoon. Can you please update to it and get in touch via Premium Support if this persists.
The automatic Plugin update engine via the Dashboard > Updates screen is distributing the 2.1.10 Plugin update to users so it is safe to use. A series of very unfortunate incidents made the 2.1.8 update fail so spectacularly. If this issue persists for any users after updating to 2.1.9 or 2.1.10 please get in touch via Premium Support so we can look at this together.