I wholeheartedly believe that just having them as additional challenges each week was the way to go. I see a few predictable issues with making them recoverable. I'm sure there are bound to be more, but I'll list a few that come to mind right away.
Potential Issue 1: Progress towards a single challenge applying to every matching challenge. This could either auto-clear all copies of a specific type (such as kill 500 enemies) in the recovery queue or it could apply progress to them all, clear the active one, then all the rest become incompletable.
Potential Issue 2: Having 2 of the same challenge recover at the same time, both clear at the same time and the player only getting credit for one.
Potential Issue 3: After clearing a challenge, all of the matching challenges vanish out of the recovery queue without giving credit.
All in all, the original method of these being non-recoverable permanent challenges OUTSIDE of the usual weekly/daily challenges was the way to go since it would reward active players while simultaneously not negatively impacting those who are inactive or join late. Feels odd to be rug pulled so hard on this out of nowhere.
Edit: Lots of typos.