ANECDOTAL UPDATE
Just for laughs, I thought I’d try some common workarounds, like hovering on the DEFIANCE/PRIME thumbnail and adding to playlist. Then going to playlist, I get the season one page, with ep 1/pilot “unlocked” (I own this); but all other items locked.
https://www.amazon.com/gp/video/detail/B00C0OMIRW/ref=atv_hm_wat_8_c_8hDZMv_1_11
Season 2 and 3 menus are locked.
So, there are [2] distinct versions of DEFIANCE showing in PRIME; the “free with Prime” with Prime logo, and the lock icon buy version.
Looks like what is happening is the free to watch with Prime version totally gone, broken, retired Feb 1. and using the add to playlist, redirects to the buy/owned version, via the URL above.
I am guessing either the rights expired (it’s still on Peacock), or Amazon has the two iterations cross linked somehow. I sent a feedback note via the buy/season 1 version page; but that is a deep maybe on anybody doing anything. I don’t have free brain cell to go through the customer service route, but that might be option for anybody wanting to capture/download from legal account. I already own all season on both disc and digital, so not going to be me.
All things being equal, if I had to guess; I think it likely the rights expired Feb 1. However, that would have been a very short run since the only added that back not long ago.