As explained in #4 after your SENEC.Home System has been updated (remotely) to REVISION MCU 0825 by SENEC (without asking) the previously available statistics data is not available any longer in the default integration.
As also described in #4 you have the option to install an additional Integration Entry WEB.API: mein-senec.de Portal (usable with all SENEC.Home variants) - you need to update the integration 3.0.6 or higher (any 20YY.MM.N Version will work as well)
So then you are facing the challenge, that you have old sensor data (before the 0825 update) and the new sensor data that you might like to display together...
My personal current solution is to edit the Energy Dashboard in the following way:

and add for all the four fields the new sensors - so it looks like this (please note, that I have used senecw as my WebAPI Integration name (the default is senec_WEBAPI) - after you edited the dashboard configuration it could look like this:

Now you see on the Energy Dashboard your "old" and "new" data together... (yes in slightly different colour shades)
So yes - the old sensors are still reported as "missing" - but IMHO this is a valid compromise - if you have alternative ideas (or opinions) - please feel free to share!
Update - for advanced Users:
@loeffelpan have provided information how you can manipulate HA's SQLite-DB (#17).
In the initial post you will find a link to an initial Windows PowerShell script (that you must adjust to your local setup/needs) that allows you to add energy data from the past to your energy dashboard.
Additional there are instructions how to 'join' energy data from old and new sensors (#17 (comment)).
As explained in #4 after your SENEC.Home System has been updated (remotely) to REVISION MCU 0825 by SENEC (without asking) the previously available statistics data is not available any longer in the default integration.
As also described in #4 you have the option to install an additional Integration Entry WEB.API: mein-senec.de Portal (usable with all SENEC.Home variants) - you need to update the integration
3.0.6or higher (any20YY.MM.NVersion will work as well)So then you are facing the challenge, that you have old sensor data (before the 0825 update) and the new sensor data that you might like to display together...
My personal current solution is to edit the Energy Dashboard in the following way:

and add for all the four fields the new sensors - so it looks like this (please note, that I have used

senecwas my WebAPI Integration name (the default issenec_WEBAPI) - after you edited the dashboard configuration it could look like this:Now you see on the Energy Dashboard your "old" and "new" data together... (yes in slightly different colour shades)
So yes - the old sensors are still reported as "missing" - but IMHO this is a valid compromise - if you have alternative ideas (or opinions) - please feel free to share!
Update - for advanced Users:
@loeffelpan have provided information how you can manipulate HA's SQLite-DB (#17).
In the initial post you will find a link to an initial Windows PowerShell script (that you must adjust to your local setup/needs) that allows you to add energy data from the past to your energy dashboard.
Additional there are instructions how to 'join' energy data from old and new sensors (#17 (comment)).