gamerule command not working

I was playing in a new created world and setting up the gamerules and noticed that it shows that the gamerule changed(it also shows the value i setted when i checked with /gamerule) , but it wasnt working. when i checked the level.dat nbt, it didnt change anything in there.
i tryed commandblockoutput, keepInventory and gameLoopFunction.
all of then arent working so i think the whole systhem is broken.