The definition of \zdotfill uses \pdfsavepos without checking if luatex is being used like zref-savepos does. Here's an example that errors with luatex.
\documentclass{article}
\usepackage[dotfill]{zref}
\begin{document}
text\zdotfill text
\end{document}
The definition of
\zdotfilluses\pdfsaveposwithout checking if luatex is being used like zref-savepos does. Here's an example that errors with luatex.