Could we take another look at the relationships around Knut Sweynson (Harthacnut I)?
Geni currently says Harthacnut was son of Sveyn. A curator note for Sveyn says "There is no proof that Sveyn is son of Sigurd."
I'm not sure where anyone says Sveyn is a son of Sigurd.
1. Adam of Bremen (11th century) says Harthacnut was son an otherwise unknown king Sweyn.
2. Ragnarssona þáttr (13th century) says Harthacnut (not Sveyn) was son of Sigurd Snake-in-the-Eye, one of the sons of Ragnar 'Lodbrok' Sigurdsson King of Denmark and Norway.
3. Saxo Grammaticus (13th century) says Harthacnut was son of Erik, a descendant of Ragnar Lodbrok, by Gudorm, a granddaughter of Harald Klak.
So where does the idea come from that Sveyn was the son of Sigurd? The two profiles don't yet have any kind of organized presentation, so the answer could be there but if it is I'm not seeing it.