To reproduce the problem, add some xlsx files with dates with at least two different months, an account key, and an amount in two different folders; then, create three different queries in a dataflow using the two sources and disable all three of them, finally append the three queries into one new query and load that one. All of this has to be done in a pro workspace, not premium.
What happened was that in the Dataflow, data for an account key 41050 appeared for June 2023 in the very last step, but on connecting to it in Power BI, this data somehow shifted to May 2023. The data for the other account keys seem to appear normally. Just by copy pasting the query in Power BI instead of connecting to the dataflow resolved the issue. Which is very strange.
