Connectors are usually the first place to look.

I usually start by cleaning the edge connectors with a pink rubber eraser.

Since two displays are affected in the same group, that usually indicates a common issue at the MPU or MPU connectors.

http://pinwiki.com/wiki/index.php?title=Gottlieb_System_1#Display_Data_Problems

Move the displays around to see if the problem follows. If it follows then it's the displays, (not likely from your description) if not, then its in the mpu as force said. (don't have Hulk or I'd tell you what chips to check but, if you have the schematics you can find them easily.)

No. The driver board has nothing to do with the displays. They are operated by the MPU.

Nope, display drivers are along the right edge.

You are missing segment B. This comes from A1J2 pin 14 which is driven by IC Z17.

But one display can load down the other. So, with power off, unplug player 3 and power back up and see if player 4 is okay. If not, power down, unplug #4 and plug #3 back in and power up. If both bad, it's probably Z17 unless you have a bad pin at 14.

May not be the solution, but....
I had issues with my Gottlieb Hulk displays. Thought it was the mpu (bought with solder on the contacts to help make the connector "fit"), so got a Ni-Wumph. Helped, but still had display issues, including the credit/ball display. Found a used 4 digit display on eBay and plugged it in. Everything now works great! Your mileage may vary, and this may not be your issue, but on the off chance!