Long title on one line

The flux theme is not behaving well when breaking long lines.

The same goes for subtitles, which are usually longer.

While it is being fixed you can use this workaround:

title{ Huge Duis aute irure dolor in reprehenderit in [0.5em]   Huge voluptate velit esse cillum  [0.5em]  Huge dolore eu fugiat nulla pariatur[0.5em]}

subtitle{ Large lorem ipsum dolor sit amet, consectetur adipiscing elit, [0.3em] Large sed do eiusmod tempor incididunt ut labore et [0.3em] Large dolore magna aliqua}

Note (not related with the question)

To me the result is nicer if you replace the fonts recommended

% Use roboto Font (recommended)
%usepackage[sfdefault]{roboto}
usepackage{mathpazo}
usepackage{helvet}

I did not use your template, so I can't guarantee this will work, but there is no reason why it should not.

Just use a stack to construct the title and subtitle. I also show how to set the respective baselineskips, if the default is not correct.

If the top margin seems wrong, try a Longunderstack instead of a Longstack.

documentclass{scrreprt}
usepackage[usestackEOL]{stackengine}
title{setstackgap{L}{22pt}% Set baselineskip if needed
  Longstack{Duis aute irure dolor in reprehenderit in 
  voluptate velit esse cillum  
  dolore eu fugiat nulla pariatur}}

subtitle{setstackgap{L}{16pt}% Set baselineskip if needed
  Longstack{lorem ipsum dolor sit amet, consectetur adipiscing elit, 
  sed do eiusmod tempor incididunt ut labore et 
  dolore magna aliqua}}
begin{document}
maketitle
end{document}