I am sorry if this should be a duplicate, I only found MC-55686, which was maybe caused by this.

Relates to: MC-55686

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.

Affected blocks:

• Sign (Text)
• Command block (Last Output)

Command used:

/clone ~ ~ ~ ~1 ~-4 ~100 ~ ~-4 ~2 replace move

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