In this post, I will propose two possible candidate ethnic groups for the speakers of that language. The following text is a Manchu-language description of groups of people called Fiyaka and Kiyakara who brought tribute to the Qing:
fiyaka, fiyaka sunggari ulai dergi ergi ten i bade bi, mederi tun i jakarame son son i tembi. nimaha butame gurgu buthašame banjimbi. hahasi hehesi gemu indahūn sukū be etuku arafi etumbi. juwari forgon de nimaha sukū i arambi. banin doksin becunure de amuran. tucire dosire de kemuni jeyengge agūra gaifi yabumbi. aniyadari seke jafambi.
kiyakara, kiyakara huncun mederi, jai fucin yose i jergi birai biturame son son i tembi. haha hehe gemu ferten de muheren etufi jurhun isire menggun teišun i araha niyalma be miyamigan obume tuhebumbi. hahasi buhū i sukū be mahala arambi. bosoi etuku etumbi. bethe niohušulembi. hehesi funiyehe be tuhebume, sifikū sifirakū, adasun de halai hacin i šeoleme wangnambi. boo ūlen jahūdai weihu be gemu alan i weilembi. ese asu baitalame bahanarakū. nimaha šakarame gurgušeme banjimbi. banitai heolen sula iktambume asaraha hacin akū. ceni ba i ici gisurere be kiyakaratambi sembi. aniyadari seke jafambi.
"The Fiyaka. The Fiyaka are in the high places on the east side of the Sunggari river. They are scattered along the island(s) of the sea. They make their living fishing and hunting. Men and women all make and wear clothing of dog skins. In the summer they make them from fish skins. By nature they are cruel and they love to fight. When they are out and about they walk carrying bladed spears. Every year they bring sable as tribute.
"The Kiyakara. The Kiyakara are scattered along the Hunchun Sea, and along such rivers as Fucin and Yose. The men and women all wear rings in their noses, and hang figurines as ornaments made of silver and copper as much as an inch long. The men make hats from deerskin, wear cloth, and go barefoot. The women let their hair down, and do not wear hairpins. They embroider their lapels with all kinds of different designs. They make every kind of house and boat from birch bark. They do not know how to use nets. They make their living by spearing fish and hunting. They are naturally lazy and idle, and do not customarily accumulate and set aside stores. The speech of their land is called kiyakaratambi. Every year they bring sable as tribute."The Fiyaka and Kiyakara occupied similar territories, as far as I can tell. Both groups are now said to have been Tungusic, but I think the evidence for this is based largely on the fact that Tungusic speakers are known to have lived in the areas they inhabited. The same section of the tribute records also mentions Nanai (heje) and Udeghe (nadan hala), as well as non-Tungusic Ainu (guye or kuye) and Nivkh (kilen).