There's a closest approach line on the screenshot, so I can't figure out what the bug is...
Now if you intend to dock, you should not put your ship on the same orbit as your target first. If you do that, the 2 objects will orbit at the same speed, so none of them will catch up with the other. That's the reason why the line doesn't move.
For this, you rather need to put your ship on a lower orbit. It will orbit at a faster rate than your target, and will be able to catch up with it.