Minecraft /fill no block texture glitch (usually 50% of the time)

i was making a mini-game and noticed that sometimes with /fill the iron_block didn't always have a texture therefore, replaced with the black and pink boxes. i did further research and its not just the iron block, its every block as far as i saw. such as gold_block, redstone_block, diamond_block, etc. (water/lava weren't affected)