Lovelace Sensor Card: Can't get the line displayed

Configuration Frontend
1

I am on sw Version 0.87.1 rather new with lovelace.
I have a number of number sensors integrated showing PV production and Home Energy consumption. I read them through from my SMA inverter using pysma.

For some reason I can’t get line graphs with the lovelace sensor card. It does always display and update my sensor values but no chance for the line. I tried different themes then to see if I am drawing white on white but without success.
There should be not much to do wrong. This is my config of the card, Can anybody advice??

type: sensor
graph: line
theme: default
entity: sensor.power_from_grid
detail: 2
hours_to_show: 3
unit: W
name: Verbrauch

2

Same for me most of the time !
I noticed that sometime the line is back. Maybe it depends of the device used, I don’t know at the moment since I’ve not had time to investigate more…

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