I'm having the same problem with my Warlock. I haven't seen any Corsair Down bounties since shortly after Forsaken launched in Season 4. I can find them just fine on my other characters but this is an issue since the "A Map Asunder" cannot be discarded or abandoned and is permanently taking up a slot in my pursuits on my main character. I've spent countless hours in Dreaming City hunting Scorn and even running through the Strike. Nothing seems to force them to appear after hours upon hours. I've noticed some people in other threads have reported that the Corsairbane bounty flags Corsair Down's to stop dropping while the quest is active. If the quest is abandoned or expired then the flag is not removed and no more Corsair Down's will appear on that character. This is speculation but it does appear to be a running theme among people that are experiencing the issue.