The two are the same person.
The reason why Zhen Ji is called Zhen Mi is because it is rumored in unofficial history that Cao Zhi fell in love with her and wrote "Ode to the Goddess of Luo" for her. Therefore, later generations called the Luo River water god "Mi (fú)" "Concubine", Zhen Ji is called Zhen Mi.
In Luo Shen Fu, Luo Shen is Mi Fei. Everyone thinks that Zhen Luo is Luo Shen, so she is called Zhen Mi. As for Zhen Ji, in ancient times, a beautiful woman was called Ji, and when she added her surname, she was Zhen Ji.