I know why.
Your PV energy sensor reports 0 instead of unknown when it becomes unavailable. And the SMA Sunnyboy inverters reboot on a weekly schedule (bad/lazy programming by SMA*). When the sensor returns to reporting correctly the total energy has jumped from 0 to your lifetime total, and this is dutifully recorded by the energy dashboard. If it had jumped from unknown to the usual total the energy dashboard would have ignored it.
See this topic for some additional info on how to create a filtered sensor with an availability template thatyou can feed to your energy dashboard to correct this:
https://community.home-assistant.io/t/how-to-prevent-entity-from-resetting-to-0/369363/2?u=tom_l
In short: create a filtered template sensor or wait until this SMA integration issue fix gets merged into Home Assistant.
Honestly, I would create the filtered sensor anyway, just in case other issues with the integration pop up in future. I’m not removing my filtered sensor once the fix is merged.
* so much for excellent German engineering 