Maciamo commented in the U5 entry of this site (in the genetics section) that there was U5b1b1 haplogroup among NW sub-saharan Africans.

According to YFull https://www.yfull.com/mtree/U5b1b1b/
It's just some centuries old.
Which leads me to think it has to be some back migration of people from al-Andalus into the Magreb.