A potentially good movie ruined by a completely implausible premise

Rating: 2/10 (26 March 2019)

For the first 75% of this movie, I was tense, on the edge of my seat and intrigued -- everything a person is supposed to be watching a horror/suspense movie. The acting was great, especially as everyone in the film basically had to play two very different characters. The soundtrack was perfect. Then came the big reveal of the underlying cause, and it ruined everything. As my friend and I were leaving the theater, we looked at each other and simultaneously said, "Wow, that was really dumb."
Spoilers below
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The makers of this movie would have us believe that clones were made of, well, apparently everyone in a network of underground bunkers, and that the clones and bunkers were there, presumably using electricity and generating sewage, for thirty odd years without anyone above ground ever noticing. The clones were "tethered" to their above ground double, meaning that any movement made by the above ground person was mimicked by the clone. This was driven home by showing clones mimicking people riding roller coasters and other amusement park rides during one bunker scene (btw, the actors doing this scene were truly awesome). Nyong'o's "tethered" character talks to her counterpart about being forced to be with the "tethered" husband and have children because the above ground version of her character married and had children (for reasons I won't get into, this also runs contrary to the premise). The son even uses this property to dispose of his clone. Heck, the stated reason for the clones getting all stabby was to "untether" themselves from their above ground doubles and be free. In other words, one of the basic premises of the movie was that the clones didn't have much, if any, free will when it came to how and when they moved.
That said, the film doesn't even attempt to explain how the clones were able to avoid the "tethering" when the time came to get all stabby, i.e. the above ground people, who the "tethered" clones had to mimic, weren't running around stabbing people, so how could the "tethered" clones do so?
I'm willing to suspend my disbelief for pretty much anything as long as the writer sticks to his premise. Here, all the action in the movie was counter to the stated premise, which, in my opinion, ruined the whole thing.
Also, and this is a minor point, the tethered people apparently survived in the bunkers after the scientists abandoned the experiment by eating rabbits. However, despite there being bunnies all over the place in the bunker scenes, there was never any sign of anything the bunnies could eat and no plausible means for the "tethered" clones to acquire such.
Another minor point, but every clone shown during the stabby part of the movie had identical scissors. Where could they possibly have gotten them? Are we supposed to assume that the scientists who abandoned the clones also left behind millions of scissors?
Finally, I'm not going to ruin the "big" twist at the end, but it was completely predictable and, although the music and the actor's facial expressions indicated that I was supposed to be freaked out in some way by it, it was of absolutely no consequence and changed nothing.
In short, great acting, great soundtrack, awful writing.