How to fix common error causing multiplexed LED segments to flash and dim
To prevent the brightness of the display from &quot;jumping around&quot; (flashing, actually) based on how many segments at a time are lit, the right answer is that every LED should have its own resistor.  The following LTSPice trace shows how it improves performance by maintaining full brightness when the two LEDs are on at the same time (small amount added to I(D4) to offset the trace for improved viewing):

Each LED really needs to have its own resistor.