Compile this MWE with LuaLaTeX and with XeLaTex
\documentclass{article}
\usepackage[defaultfeatures={Kerning=On,Ligatures={TeX,Common,Rare}}]{libertinus}
\begin{document}
\begin{tabular}{ccccccccccccc}
ff & fi & fj & fl & ft & ffi & ffj & ffl & fft & Th & ts & tt & Qu
\end{tabular}
\end{document}
The result for XeLaTeX (note the Qu-ligature):
The result for LuaLaTeX (note the missing Qu-ligature):
Expected result: The Qu-ligature should be there. What am I doing wrong? Is this a bug and if yes, is there a workaround until it is fixed upstream?