Time to reflow the solder joints on each Connector pin on each display circuit board. Also, reflow each plasma display lead on the circuit board.
After this, if you still have a problem, time to wiggle the wires going into the connectors with all displays installed and the display test cycling. Alternately, you need to trace the daisy-chained data lines between diisplay boards. There is likely a bad crimp or broken wire at a crimp-on terminal.