Why do Custom Icon Backgrounds Sometimes Not Appear

[hellyars]

This question pertains to custom icons.  

I created a custom icon in Pixelmator Pro (or Affinity Designer).  The dimensions are 171x171 pixels.  The image is exported as a .PNG.

The icon appears correctly in Interface Designer.  However, the background disappears when the macro is added to a workflow.  This has happened with a number of icons I have created, but not all (and all have been designed to the same 171x171 dimension and .png formal).  Reference images below...  Any explanation? 

[hellyars]

Issue seems to be isolated to solid background colors.  It works if I add a fancy background effect.  Go figure. 

[TayTay]

I'm having the same issue.

[TayTay]

I found a solution by going down to a 65x65 size.