When you place a sign and destroy the block behind it, the sign disappears as it should. The problem however is that when you place a chest where the sign was, the sign appears again. The chest’s hit box is present, and when you right click on the sign, it opens the chest GUI. I have not been able to recreate it elsewhere. To get the fill clock, put “/fill ~-1 ~ ~ ~-1 65 ~ redstone_block 0 destroy” into a command block. Then, under the lowest redstone block in the clock, place another command block with “/fill ~ ~1 ~ ~ 65 ~ glowstone” in it. Replace the first command with “/fill ~-1 ~ ~ ~-1 65 ~ redstone_block”. In the same chunk, I have a particle command, a few testforblocks commands, and clone commands when the testforblocks commands are true.