Most likely, you forgot to enable the "Composite on Original" checkbox at the very bottom of the effect.
With it enabled, you can have several copies of the effect on the same layer. No need to duplicate the layer.
Only for the topmost effect, you maybe don't want to check this "Composite on Original".
Alternatively, you can combine the different layers with blending modes.
For these basics, I recommend my Guru Lessons.
Already in part 1 blending modes are shown, part 2 also includes the Advanced Lightning effect.
I clicked on the checkbox, however, now my whole layer is only showing the white solid. When I uncheck the box I can see everything again.
Did you ensure to have all duplicates of the effect on the same layer? Did you also ensure to have the option checked for all lightning effects on this layer except the first one?
If it still does not work, a screenshot could help to understand the issue.
The second one needs the checkbox checked and the first one not. You have it the other way around.
Very strange that it didn't work before. I got this to work.
Now I want to duplicate these individual lightning effects and transform them horizontally so they appear on both the left and right sides. However, after selecting them, duplicating them and using layer > transform > flip horizontal they flip horizontal, though the original ones are no longer there. I'm guessing this is similar to my original problem? What did I do wrong?
If you have all effects on the same layer, flipping the layer means flipping all effects on the layer. I suggest that you move the origin of the Lightning instead of flipping the layer. Otherwise your you need two layers - one for the flipped ones and one with the other ones.