Embedding multiple vaadin apps in one HTML page not working

I’m trying follow the Book of Vaadin https://vaadin.com/book/-/page/application.embedding.html section on embedding Vaadin apps, but can’t get it to work as documented.
I would like to have a single appPage.shtml file (attached) with all the vaadin servlet references and then use appPage.shtml as an include’d template page using SSI.

If I define more than 1 vaadinConfigurations entry the Vaadin app is not displayed. If I define just 1 entry then it works fine.

Here’s what I’m using:

Full version of the above file is attached.

If I use just one of these then it works fine. If I have both defined, I get nothing inside the HTML page where I put:

I can successfully run http://localhost:8080/app/home and http://localhost:8080/app/register directly in the browser URL bar.

I’ve tried the above with both Chrome and Firefox (both latest versions).

Any suggestions would be greatly appreciated.
12438.xml (1.88 KB)
12439.html (2.97 KB)