Solving a Data Studio report anomaly

I noticed a fairly standard report wasn’t giving me the figures I expected. As always, I validate a DS report by comparing with Analytics, and often also with the GA Query Explorer. And yet I could not see why my DS report was wrong!

An out-of-place segment or filter was the obvious reason, but I had neither, so it wasn’t that. But then I got to thinking – I have NO segment applied to the report, and sure enough, when I added the standard segment ‘All users’, the report was back to being accurate!