"Opens a File" links broken on different Mac - OmniGraffle 6

Using OmniGraffle 6.4.1

I have this directory:

I’m creating a link to testFile.txt by dragging the file onto OmniGraffle object.

  1. All seems to work and I can open the file.

  2. When I move the project directory into another directory, on the same computer it all works fine and I can still open the file.

  3. When I copy the directory to another computer, the links stop working.
    I can see the file Path in the inspector is still correct, but the Omnigraffle no longer opens the file.

To fix this I had to re-drag the file to create a link. The path doesn’t change in the inspector, but now the file opens.

Any tips of why this is happening?