You don't actually read the stuff you link to.
The first article mentions an aggregate of polls showing a loss of Black support for Harris, but links to another article. And that article talks about one single small poll.
Harris will get about the same percentage of the Black vote as prior Dem nominees.
BTW, if an article talks about one ethnic group without mentioning changes in others, you are provided with an incomplete picture. For example, Harris is picking up support among women voters, but may be losing support among Latinos.