I can't remember the specifics right now but there are special rules for South Africa as well. I suspect that's the actual issue since you can do it without ZA in the itinerary. Since you're going via DOH anyway, test it with some of their other Southern Africa destinations that isn't South Africa. I'm pretty sure Zambia, Zimbabwe, and Mozambique remain, but Namibia is going away sadly. It's not exactly cheap to buy a separate ticket in the region but depending on what miles / points you have at your fingertips might still be ok. SA miles actually are useful for short haul flights but unless you've built some up before I don't know that helps you, they aren't a Marriott partner anymore sadly. It REALLY stings losing that BA franchise in JNB since that was the only OW option in southern Africa. HRE-JNB isn't terribly priced in economy with UA miles, but CPT isn't close enough to get the discounted rate. If you have G6 (GOL) miles then actually intra-Africa on ET is pretty cheap too, even in business class. I know these aren't exactly mainstream programs but might be a future strategy if you want some cheap mileage flights in the region. QR Avios are also great near Rwanda, but not so much as far flung as South Africa. (Also QR doesn't fly to KGL anymore, they turned the DOH route over to their close partner WB (Rwandair) on a 737 at that).