I'm only speculating, but serious blood clots are also known to be possible side effects of some forms of hormonal birth control. Given the relatively young ages of the women who had side effects on J&J, I would be really interested in learning if there could be a connection there.

They aren't - at least one out of nine patients with blood clots from AZ vaccine was male [1].

[1] https://www.researchsquare.com/article/rs-362354/v1