The self-published-template generates HTML that's not correctly shown in the HTML output of wiki2book.
Example
Foo<ref>Some source{{self-published source|date=September 2020}}</ref>.
== References ==
<references/>
It should look like this:

But it looks like this:

(the empty braces are the problem here)
The
self-published-template generates HTML that's not correctly shown in the HTML output of wiki2book.Example
It should look like this:

But it looks like this:

(the empty braces are the problem here)