How to chain combobox Export Values

I'm going to straight up admit I do not know scripting language so everything I've used I have found from the web.

I have 3 comboboxes in a PDF with choices I want to have linked.

I would like my export value of "Combobox1" to be the item value of "Combobox2", which then pushes "Combobox 2" export value to item value of "Combobox3".

I am using this Custom Keystroke Script (under "Format" tab) for "Combobox1":

if(!event.willCommit) {

  this.getField("Combobox2").value = event.changeEx;

}

This successfully pushes the export value to "Combobox2" (where I've set all dropdown item value options to the "Combobox1" export values). However, once I add any export values for the options in "Combobox2", the script from "Combobox1" no longer works.

The script only pushes to "Combobox2" as long as "Combobox2" options have blank export values. I don't understand why this happens, as I would like to then use the above script to push "Combobox2" export values to "Combobox3". Is there no way to repeatedly chain import export values?

Can someone please help? I am using Adobe Acrobat DC FYI

Thanks in advance!