The translation of שָׂנֵא (sane) as "unloved" is frequent in more modern translations in many places such as Gen 29:31, 33, Deut 21:15, 16, 17, Prov 30:33, etc.
There is a similar Hebraism in Luke 14:26 -
- “If anyone comes to me and does not hate father and mother, wife and children, brothers and sisters—yes, even their own life—such a person cannot be my disciple. See also Matt 10:37.
This is despite the explicit instruction to love one another (John 13:34, 35) and to "honor your father and mother", Matt 15:4, Mark 7:10. Thus, the Hebraism to "hate" can sometimes mean to simply love less than another person.
In the case of Jesus' comments about hating father and mother - He clearly intends that we simply love Jesus supremely - more than Father and Mother and that in the Hebrew mind this is "hating father and mother" compared to Jesus.
The same is true of Leah and Rachel. Jacob love Rachel but "hated" Leah, that is, he loved her less. [Note that if Jacob actually hated Leah, he was able to divorce her but that is another matter.]
This is why the modern version say, "unloved" in Gen 29:31. The fact that Jacob buried Leah in the family cave of Machpelah (and Rachel was not) shows that Jacob did love her to some extent.