Suppose you have four filaments going through the same nozzle. Switching between filaments requires priming the new filament, so a prime pillar is needed. Suppose you would like to print three filaments in a single layer. That means two filament switches within each layer, which means two priming operations within the prime pillar for each layer.
Unfortunately, it seems like the prime pillar can't handle more than one filament switch per layer. Take a look at this screenshot:
In this screenshot, when the filament was switched from blue to green, the green filament was properly primed within the prime pillar. However, when switching from green to yellow, the yellow filament was not primed within the prime pillar at all and was printed without any priming (see the innermost circle).
Could I be doing something wrong in my prime pillar setup or is this a current limitation for Simplify3D? I have three separate processes for the three colors. Each process is set to use the prime pillar for all extruders.