The KDP forum is useless. Worse than useless.

I have done about 8 or 9 books now with KDP with the occasional problem. Once they did not let me publish because they did not like when I started numbering my pages.

I have no idea why your covers are not going through. I assume you have followed their instructions with bleed and spine dimensions.

If you click on Help in KDP you have the option (on the lower left side of the page) to Contact them by mail or by phone. Mail usually works and they do get back in a day or two.