I am posting this in case there is some incompatibility between GeneratePress and the WP Logo Showcase Responsive Slider which does not work as expected using the GeneratePress theme. The issue is described here in detail.
If this is caused by GeneratePress, is there a workaround?
Well, it might be theme-related as in Twentyfifteen and TwentySeventeen, it operates correctly (it still shows bullets but at least spacings are correct). The problem I see is that the li element containing the image is set smaller than the image itself, which results in images sticking one to another (which happens in GP but not in the TwentyX themes). So it seems like a plugin/GP incompatibility but it’s probably the plugin author who should take a look at this. I will let them know.
For the time being, I did use another plugin to get the job done.