After updating to 1.6.1 (and regenerating CSS + Clearing cache) my nestable sliders are no longer displaying in the backend. They work fine on the front end.
Yes, the converter gave every image in every slider a fade-in interaction.
Slider not showing was due to the code provided here, to fix the flickering of entrance animations.
Once I remove it, sliders show up. So no bug / bug related to flickering animations.