Normally if you create a ChildActor in a blueprint, the only setting in the “Child Actor Component” section of the details panel is “Child Actor Class”. Once you select the child actor class, the “Child Actor Template” section shows up below it.
If you copy and paste a ChildActor, the “Child Actor Class” will be selected, but the “Child Actor Template” section is not visible and the settings are not copied. You need to re-select the child actor class for it to show up, and then manually copy the settings over.