Category filter is not showing?

This could be a reason why the filter is not showing:
If only one category has images assigned, the filter will not display. For the filter to appear, make sure that multiple categories have images assigned. The filter becomes active when there are multiple categories with images for users to select from.

Resolution:
To resolve this, assign at least one image to each category you want to display in the filter. Once this is done, the filter will work as expected.