Can’t activate more than one slide

If activating one slide disables another, switch the Slider Type from "Hero Scene" to "Standard Slider".

A Hero Scene slider is essentially a “one slide, slider”, so even though it’s possible to have multiple slides created in the slider’s admin, because only one can ever be officially shown inside the slider, only one can have an “active” status.  And this is why “activating” one slide automatically disables the previously activated slide, because only one slide can ever be officially “active”.

The solution for this is to change your Slider Type to “Standard Slider”.  A “Standard Slider” is a slider that can have more than one slide, so making this change will allow you to officially “activate” more than one slide at a time.

And then all of the slides can be officially activated: