Hi, sorry for not responding sooner, I was pretty swamped with other things.
It seems you're right. I did the steps again as you outlined in your post, and now everything works fine. I must have previously done something wrong. Thanks again for your help, and sorry for wasting your time馃槄
One thing to note, though, is that I couldn't just extract the example project, copy in the addons, and build the project. Godot would throw an error because the plugins were already enabled in the project.godot. The error message is sadly obscured by Godot's 'Building project' popup:
After getting this error, attempting to build again will still fail, even with the addons disabled. I need to re-open the project, and then I can build the project and enable the addon. Perhaps it would be good to initially disable the plugins in the distributed example project? Just a suggestion, feel free to ignore if this is not feasible for some reason.