Minor bug:
In your blueprint, if you already have a category called e.g. “MyCategory” (no space), and then you add another variable into that category by dragging a variable into it (in the My Blueprint tab), then it correctly moves it into that category in the My Blueprint tab, BUT it has actually created a new category called “My Category” (with a space). If the variables are exposed and you place that actor in the world, you’ll notice there are two categories in the actor properties tab called “My Category”.
The expected behavior would be for it to look up the proper existing category name (without the space), when you drag.