Chicken farm lava bug

I have built two different auto chicken farms, however, both of them have not worked. They both should have worked, as I got them from tutorials on Youtube. These designs both used the half slab concept, where the chicken eggs are dispensed on to the slab, and grow up from there. However, when the lava was triggered, the adult chickens were able to survive the lava and were not affected. I have tested this in survival and creative. Youtube tutorial for one of the designs here: https://m.youtube.com/watch?v=bm99P6UOzKg