target-counters do not find IDs containing a dot, so the method returns 0. Unfortunately, dots are valid characters in IDs in HTML5 (which i find quite ugly). Therefore dots need to be escaped before they are passed to a query selector, e.g. #te\\.st.

Example:

<a href="#paged.js">Paged.js</a>

...

<h1 id="paged.js">Paged.js</h1>

a::after { content: target-counter(attr(href), page);}

Result: