ROBIN MARK D'ROZARIO
Off hand I can only suggest the reason is that you haven't created a Merged / Stamped layer as the first step of the macro.
Affinity is a beautiful program and is probably 99% Photoshop, unfortunately the remaining 1% is where 99% of the PPW resides.
Writing macros is Affinity is great if you like High Blood Pressure. The implementation of channels and apply image in Affinity means extra steps and alternative thinking to get what you want. The macro editor is also strangely hamstrung, for example , one can normally rename a spare channel in Affinity except when you create said channel while writing a macro!!
Since you mention the Bigger Hammer I have uploaded an Affinity version to the files section, the folder is called Affinity Photo Bigger Hammer. It was made 7-8 months ago and I haven't used Affinity much since then so it hasn't been tested extensively. To import it use the following pathway View > Studio > Macro.
After running it please turn the Original Colour and Darken layers down to 50% opacity, I forgot to do this.
You are then presented with five options of the Hammer - R, G, B, RGB and RGB desaturated. Each option has a nested Smart/Live Filter layer for Gaussian blur to adjust the radius. Choose the one you like and delete the others to reduce file size. You could also experiment with running two blur channels at the same time.
Robin Mark D'Rozario