I've been trying to book a multi-city flight ARK-ZNZ-(DAR)-NBO in Nov on PW through alternativeairlines.com and their call centre for the past 5 days!
It is definitely much cheaper than ARK-ZNZ and ZNZ-NBO combined. It is priced as a one way ARK-NBO flight with a stopover at ZNZ in N fare. This N fare does allow unlimited stopovers, therefore I doubt it's because of illegal routing.

Every time the agent confirmed the itinerary, PW canceled it the next morning, even after the e-ticket was already issued. Now the agent is trying to rebook the 4th time, but I am not very optimistic...

Luckily I go to checkmytrip.com all the time, otherwise I'd end up in ARK with no seat! This is the most ridiculous booking experience I've ever had. I guess if the TA cannot get this resolved, I'd better pick another airline all together.