Thanks
@MevetS and
@mrj412.
While answering your questions, I figured it out...
Because of bluetooth issues and cos as a dev I tend to install all sorts of things, I decided that this MacMini would be a clean machine. iCloud data (AppleID) was shared between this and my older machine, and I have a licence for Setapp for three machines.
I decided to look at where iStats keeps its database for the historical data:
~/Library/Application Support/iStat Menus/databases
That file was exactly the same size as the same databases file on my other Mac, which is strange. So I decided to delete the database on this machine and restart.
Now the data only shows history for the last hour.
Question is how did the iStats Menus database get copied from one machine to the other? I reckon it was one of the /Application Support/ folders that I copied over, knowing that I'd want the same settings and data. Didn't check inside to realise that I was copying a database file.
To double check, I uninstalled iStats Menu and it deleted the /Application Support/iStat Menus folder. Then I restarted and reinstalled iStats from Setapp, and the history makes sense now
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