Since the lamps are physically next to each other, have you confirmed they're getting 6 volts on the base of the lamp sockets where the playfield braid wire connects to both sockets?

If you look at the rectifier board schematic the spec for this switched illumination power rail is 5.4VDC but it usually measures around 6 volts.

The braid wire that connects to the base of each switched illumination lamp socket carries this power. The individual wires connected to the tip of each lamp socket comes from the lamp driver board. The lamp driver board actually switches those individual colored wires to ground when it wants to illuminate the respective lamp.

So if the base of those lamp sockets aren't measuring around 6 volts, follow the braid wire connected to them to determine if there's an open circuit.
If they turn out to be ok, then the next steps are:
Ground the individual colored wire on the tip of the lamp socket to complete the circuit path, the lamp should illuminate.
If yes, go back to the lamp driver board and ground the metal tab of Q40 to test the shoot again lamp, ground the "anode" leg of the Q21 SCR to test the 5X bonus multiplier lamp - see the pin definition below:

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