I am sorry if this should be a duplicate, I only found
MC-55686, which was maybe caused by this.
When you clone move a sign with text (maybe this affects also other NBT storaging blocks) and then place a sign at the old spot, the sign will contain the text of the old sign.
- Sign (Text)
- Command block (Last Output)
You have to place on the side of the wall facing in the x-Direction a sign with text and then on top of the wall a command block with this command
It seems like this only happens to the latest cloned signs, as soon as you clone move it again, the old ones won't work again