Going to Ori O Koiki and killing the Wahaki's leader seems to fix the issue. Upon returning to Onekaza, she will offer you the quest to ally with the Wahaki, and all you need to do is end the conversation and talk to her again to turn in the quest, since, luckily, the quest anticipates the possibility of you killing the leader and still allows you to finish it if you do. Once you finish, you should be able to proceed and sail to Ukaizo without the Wahaki. I tried to do it without killing the leader, however it seems like the only way to get the quest to trigger for now. It's a temporary fix but better than not at all.