Thought I had seen it all...
We know it doesn't matter much if you process emulsion up or emulsion down when tray processing.
But it does matter that you do it all the same in the same batch.
I just saw a ghost.
The sensitometry sheet went in emulsion down while all the rest went emulsion up. I had a hunch it happened but wasn't overly concerned.
Well it matters, significantly. When two sheets are tray processed emulsion to emulsion they compete for the same thin layer of developer.
Highest densities of the sensitometry strip exhausted the developer locally, and left a ghost of the step wedge as lighter density on the photograph next to it.
Silver lining, I don't like the shot that was ruined and none of the others was affected.