Capturing enemies is not working

I followed all the steps for capturing enemies:
I have researched all the techs and built a containment facility and it is powered on
I knocked out a siren in base defense. I have tried both using the electric shock by a technician whose (shock value?) is 180 and it is much larger than the siren’s remaining health. So it says that it is paralyzed. (some purple words showing up after it got hit)
And I cleared out all the other enemies. (It is really the last one alive, I tried to kill it and the objective is achieved)
The game does not end. The objective is still killing all the enemies.
One thing to notice is that the siren is bleeding (but won’t die in a turn)
It is so frustrating not being able to capture an enemy and actually I tried bashing on crabs before and that doesn’t work as well.
Maybe there’s something wrong to it?

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