Hello @Matty,
Thank You for posting your query onto the Forum.
Well there’s a minor correction in the formula for Cash Receipts From - Investing. In the given file the formula is mentioned as given below -
Cash Receipts From - Investing =
CALCULATE( [Cash Flow Values],
FILTER( 'Cash Flow Data',
'Cash Flow Data'[Cash Flow Category] = "Cash receipts from" &&
'Cash Flow Data'[Cash Flow Type] = "Investing" ) )
The sub-total of Net Cash Flow from Investing Activities gave the unexpected results because under the Cash Flow Type it’s mentioned as “Investing” rather than “Investing Activities”. Now since the formula for “Cash Paid For - Investing” was written correct the sub-total only gave the result for the payments side. Below is the screenshot provided for the reference -
You can use the formula provided below and can have the correct results as provided in the given screenshot -
Cash Reciepts From - Investing =
CALCULATE( [Cash Flow Values],
FILTER( 'Cash Flow Data',
'Cash Flow Data'[Cash Flow Category] = "Cash receipts from" &&
'Cash Flow Data'[Cash Flow Type] = "Investing Activities" ) )
I’m attaching the PBIX file of my working for the reference.
Hoping you find this useful and helps you in your analysis. 
Thanks & Warm Regards,
Harsh
Financial Reporting In Power BI.pbix (904.5 KB)