On a Pink Panther (6 digit) I have a single display that the h segment (the 1) lights up whenever the g (middle horizontal line) is lit. I followed the UDN6118 test instructions listed here: https://www.pinwiki.com/wiki/index.php?title=Gottlieb_System_80#UDN6118_and_Other_Display_Logic_Chip_Failures on Z1 and everything was as expected. I also tested for shorts between pins 3 & 4 on the glass and 7 & 8 on the connector.
The problem moves with the display.
Anyone have any other ideas? The display doesn't show any evidence of shorted or broken filaments.