@JonpriL @Candice C @JasroV 

So for fun, I decided to run a Profit and Loss Detail report for for "Last Fiscal Year" (2019) and then try the class filtering.

It worked immediately!! It even shows the class column etc without needing to turn it on.

IMHO this is a clear indication that there is no data issues, no data integrity issues or any sort of file issues.

This means that there is some sort of issue with theTransaction List by Vendor supporting classes.

Before I chase my tail any longer, can we please get 100% confirmation from your product team that this type of data slicing and dicing is supported by this report for the version of QuickBooks I am using? 

Many thanks in advance.