I'm not entirely sure if what I'm about to say is true or not but it feels true based on what I have experienced ingame so far.
When hunting for doja chips in Inferno for example, I always find them on mobs that are not part of any quest. If any mob is part of a quest, they never drop doja chips for me.
For example, there are various quests in Inferno where you have to kill 5+5+boss of some type of mobs such as special spiders or special somphos(spl?) and special spirits and so on. None of these ever drop doja chips and are a waste of time it seems.
I have farmed 6ish inferno chips for my doc so far and the kill-count per drop was something like this: 5(Somphos logee's), 25(somphos Logee's), 150(mixture of unredeemed mobs, logees, spiders, demons, chimeras, quest-mobs), 35 (infernal demons and logee's), 200+(quest mobs of all kinds and random mobs of all kinds), 500+ (no quest-mobs, only random mobs such as hecklers, logee's, spiders, demons and so on).
Not in a single one of these farming sessions have I found a doja chip on a mob that is involved in any questline. I have only found on Logee's and infernal demons.