No. Last change yesterday…
Well that’s just weird and I can’t explain it. Database corruption? Any relevant errors in the log?
Unfortunately I’m new and not familiar how to check database or logs, yet. 
When I hoover over the graph, I see just a number, on both graphs:
Well that blows my other theory out of the water. I was thinking the bottom graph could be from yesterday morning.
Click the info button in the developer tools menu (lower left menu, looks like an ‘i’ in a circle. A summary of the log is there.
What happens when you hover the mouse over the actual line of the bottom graph (you might have to try both the top and bottom of a step/corner in value). Clicking on the title of the graph will expand it to make this easier.
10:11 is a minute before the last entry in the upper graph. Last value reported there is 10:12 o’clock.
Disconnected: Did not receive auth message within 10 seconds
10:11 components/websocket_api/http.py (WARNING)
Got unexpected response: None
01:51 components/updater.py (ERROR)
cpuspeed: Error on device update!
00:51 components/sensor/cpuspeed.py (ERROR)
You are using a custom component for hello_mqtt which has not been tested by Home Assistant. This component might cause stability problems, be sure to disable it if you do experience issues with Home Assistant.
00:51 loader.py (WARNING)
Not sure what you ask me to do. I have hovered over the graphs to get the small screenshots…
Click on the graph heading to expand the graph.
Hover directly over one of the corners of the line where it steps in value on the lower plot. Either at the top or bottom of the step in value you should get a time and date for just that sensor, not both as in your previous screenshot.
Like this:
Looks like you are going with lovelace? When I open that, the curves do not appear and the switches for the group itself are visible. But that’s one of the next things I have to look at:
But regarding the two graphs: The second one has gone 
And all I have changed is to have opened lovelace UI - with no graph. Last HA restart was late evening:
Yay! Problem solved AIBM 
Also I meant click on the sensor text in the group (rather than the group heading, as you have done in the first screenshot) you will then get a graph pop up. Then click on the graph pop up heading to expand it. As you have done in your second screenshot.
And no, I’m not using Lovelace, yet.
Unfortunately not 
Problem is back…
And I’m not at home changing something…
No new entry in the log summary
Sorry, was on the road.
No popup on upper corner. - Popups appear only on the left edges of those tooth, when a value has changed.
Ok, That’s today’s date.
I just noticed something. Look closely at the upper graph. It’s not updating after about 1:30pm. Right about the time the lower graph starts. Something definitely changed at about 1:30pm today.
Yes, same behavior when the second graph appeared last time.
BUT: Why was the graph gone for a while as shown some threads above?! Very strange, because - as for my understanding - the graph show data from a database which isn’t changed afterwards…
I’ve seen similar things sometimes as well.
I have a bunch of Aqara temperature sensors and sometimes the same sensor results in two graphs as well.
One of them shows the temperature in F, the other one claims it shows it in °C - with the number actually being the same as in the Fahrenheit graph. Puzzled me for a while, and I put it down to the fact that the sensor reports the value in Celsius only (as I can see it in the MQTT messages), but my HA install is set up to display it in F, so HA is converting it.
Nevertheless, after a day or two, it went away I and never saw it again.
Actually, @hajo62, looking at the timelines of the first and the last graphs you’re showing, this seems to only happen for short periods of times.
Thanks…
@chairstacker: Those sensors are connected via zigbee? Are you going with a zigbee stick, or do you still run zigbee controlled by its one hub? If stick which and does it work well?
At the moment I’m with z-wave, but those sensors are sensational cheep. Haven’t found comparable sensors in z-wave…
Sound’s great.
And I do not need a zigbee gateway to configure those devices?
Just by the stick and a sensor (together for around 25€) and connect to Home Assistant via mgtt?
Yup - you need a little more kit to program the stick, though.
But all in all, not that expensive - and re-usable 