James, I did some digging and the closest thing I could find resembling this error is a typescript issue on StackOverflow.
To answer your questions:
1. Yes; I launched my site on 01/31/2021, and connected all of the Google Site Kit parameters then. I didn’t notice the issue until later in the evening when testing on the front end – as this occurs on the black admin bar on the front end while logged in. This was after the most recent plugin update on (I believe) the same day – 01/31/2021.
2. Since I am required to be logged in in order to view this asset (it’s on the WordPress admin bar while logged in as an admin), I am going to guess that I won’t see this issue while in an incognito window – which would defeat the purpose of the plugin…
3. Done.
4. Bonus. I have other, older projects on different webhosts using other domains; I will try installing Google Site kit on those to see if I can replicate the issue…
I wonder if one of the tools I’m using to keep my site running fast (aka: render blocking scripts) is causing some of the JavaScript to not render properly, which may cause it to fail in this way.