I had a file and a file-name of 71 characters, no space-character, several digits and some special 'danish' characters as well. The 'latexmk' processed the file but did not run the 'biber' sufficient times or did not run 'biber' at all; no \cite-entry was processed orderly.
xelatex, biber and xelatex were able to process the original file including every \cite-entry and the like.
When I reduced the name of the file considerably I was able to process the file in latexmk.
Is there a limit of length for a file to be processed by latexmk?