I have noticed on the LDB I make Stern MPU200 games may need a lower ohm load resistor than bally games or a couple lamps may flicker. I am using 560R. I assume it is the faster clock speed in MPU200 effects the latching nature of the SCRs. Changing nothing but the MPU software from Bally game to Stern MPU200 sometimes makes a previous 100% LDB have one or two positions flicker. Adding a parallel resistor to drop resistance 100R or so fixes them.
Also to consider is the feature lamp voltage. The more lamps turned on the higher the load will be. Which will lower the voltage so there is less current through the resistor keeping the SCR loaded. Making the LED feature lamps more likely to flicker.
I posted about this a few weeks back if you want to check it out.