DimDate / Prior Year date issue

I’ve built a performance reporting dashboard which reports on a daily basis, predominantly for comparing current year actual against current year budget. I also include prior year data. In DimDate I have a calculated column called Equivalent PY Date; which returns the prior year date that matches the day of the week in current year. Eg 01/04/2025 matches with 02/04/2024. 30/09/205 matches with 01/10/2024 (both Tuesday).

In my report pages I filter out prior fiscal year, so that only current year dates appear in my date slicer. In my prior year measures I use TREATAS and Equivalent PY Date to return the right data from the model.

Everything works fine when I use date slicers on a daily basis and can slice with all dimensions fine, it always returns the correct prior year data. However, when I add Fiscal Month into a column visual so I can drill up from Date, the prior year data for the last day of fiscal month is excluded. Eg Fiscal Month Sep, excludes 01/10/2024, even though it has Fiscal Month Sep in the same row in DimDate.

I’ve gone round the houses and nearly had a solution, but that solution then meant my other dimension slicers stopped working.

Does anyone have any experience of this and have you worked out a solution?