Understanding my Smart Meter

[MarcoS]

I try to understand the output of my P1 Smart Meter output. In the devices list I have an item named ‘Power’, with counters and usage. And I have another device named ‘Usage L1’ with just usage.
On the Utility tab the actual usage seems alike but the logs differ and I don’t understand why.

For most of the time the difference is less than 30 Watt in both directions but sometimes one shows a rise of over 1.000 while the other hardly moves. A few hours later only the other shows a peak and I have no idea why.
Can anyone explain this to me?

My Smart Meter is a Landis+Gyr E350