It looks like everything is loading.
jQuery.scrollDepth() is defined and callable.
The if you’re comfortable looking at the browser console, an easy way to see if the script is working is to go to Settings:ScrollDepth in the dashboard.
Then in the “Event Handler” section just cut-and-paste the sample function into the edit box and save.
Open a page and view the developer console as you scroll.
The scrolling events should show up in the console.
Ah… I see gtag.js
This looks like a new implementation method for Google Analytics.
I know the underlying scrolldepth JavaScript looks for Google Tag Manager, Universal Analytics, and “Classic” Google Analytics. I suspect this might be “none of the above.”
I don’t think the issue is in the WordPress plugin, but with the new recommended script from Google.
Let me check in with the folks that manage that code and see if they are aware of this issue.
Thanks for the report.