Stone not generating when lava hits water

Steps to reproduce :

make a simple stone generator ( I made one from a mysticat video)

mine away at the stone (I used an efficiency 4 diamond pick axe)

eventually stone won’t generate

 

Current results:

from time to time (not 100% of stone broken) stone doesn’t generate where lava hits a waterlogged staircase. Leaving just flowing lava into b it’s place. This causes the farm to never generate stone blocks in that place, causing it to be rendered useless. 

Expected Results : Stone generates 100% of the time