im not sure what it is but potential bug with how stairs and slabs are working

i tested it in a normal world without the addon i was using then switched on the addon and it was fine im not sure if this is a bug or just an isue with the addon it starts on y level 72 

as you see in the attached video y level 71 is fine y level 72 is not 

as you can see by the little icon thing in the corner im spam sprinting so idk

its posible that it is the type of world i generated the world today it is an old world 

but  there is still the option of the addon i was useing