Hi Martin, I think you Applied the Rotation of those ‘knots’. Or rotated them in Edit Mode…
Here’s a ground rule (with some exceptions, when you know what you are doing): always Apply the Scale and never Apply the Rotation…
So this would work when linking the Object Data:

But when you Apply the Rotation of the top one, then it’s Origin gets the same orientation as the bottom one and the Object Data says something like: ‘where are the Vertices of this Mesh compared to the Origin (of the Object)’, so when you link the Object Data of the top one to the bottom one, they also get the same rotation…Does that make any sense to you? I have a hard time explaining this.