Same issue here.
I was originally trying to get a male werewolf pregnant by alien abduction with cheats, and after a dozen tries I looked up to see if that was even possible. Turns out, occults can't get pregnant from alien abduction in the Sims 4, it seems.
A little while later, I created a new save because I wanted to start a Not So Berry challenge. Gen #1 being in the Scientist career, I figured I would try out what failed with my Werewolf and finally get alien babies (I usually never play with aliens in my game, so I really wanted to try something new).
He got abducted the normal way thrice. No pregnancy. So I started getting a little bit frustrated and tried triggering abductions with cheats. Still nothing, after around fifteen attempts again. He's a regular human Sim with masculine frame and who can get other Sims pregnant.
Moreover, everytime the aliens drop him off, he "disappears" from the screen and I can't even click on him. I have to send him to bed and he reappears when he changes into his PJs. He's also stuck with a Fear of the Dark that appears in his moodlets, but not in his traits and that I can't remove, even with cheats.
The Alien Abduction feature is totally broken.