Cyrillic text is not displayed under \paragraph (with KOMA-Script)

Question

I'v got problems with KOMA-Script and cyrillic (I guess).

Commands \paragraph (as well as \section, \subsection, etc.) don't display russian text. Is this a known issue?

I am using SublimeText, LatexTools, MikTeX and Sumatra

\documentclass[fontsize=5,parskip=never]{scrartcl}

\usepackage[paper=a5paper,landscape, left=1mm, top=4mm]{geometry} 

\usepackage{multicol}       

\usepackage{setspace}
\singlespacing% одинарный интервал

\usepackage{enumitem}
\setlist{nosep} % or \setlist{noitemsep} to leave space around whole list

\usepackage{fontspec}
\setmainfont{Arial}


\usepackage{cmap}                   % поиск в PDF
\usepackage[T2A]{fontenc}           % кодировка
\usepackage[utf8]{inputenc}         % кодировка исходного текста
\usepackage[russian]{babel} % локализация и переносы
%\usepackage{fontspec}              % otf шрифты
\usepackage{textpos}                % текстовые блоки
%\usepackage[export]{adjustpage}        % положение картинок 
\usepackage{xcolor}                 % цвет





\begin{document}




\begin{multicols*}{5}

\Large \textbf{Flush Shutter DC} \normalsize 



\large \textbf{Электробезопасность} \normalsize     %% I SEE THIS (TEXTBF WORKS WELL)
\paragraph{ПАРАГРАФ}                                %% I DONT SEE THIS
\paragraph{PARAGRAPH}                               %% I SEE THIS

text


\end{multicols*}
\end{document}

Answer 1

The document is using latin modern bold sans serif for titles and that font does not have Cyrillic.

The log warns

Missing character: There is no П in font [lmsans10-bold]:+tlig;!

You could select a different font using the classes heading setup features or generally avoid the problem with the egregdoesnotlikesansseriftitles option.

In this case you still get sans titles as you have specified Arial as the main document font.

\documentclass[
  fontsize=5,
  parskip=never,
  egregdoesnotlikesansseriftitles
]{scrartcl}

\usepackage[paper=a5paper,landscape, left=1mm, top=4mm]{geometry} 

\usepackage{multicol}       

\usepackage{setspace}
\singlespacing% одинарный интервал

\usepackage{enumitem}
\setlist{nosep} % or \setlist{noitemsep} to leave space around whole list

\usepackage[russian]{babel} % локализация и переносы
\usepackage{fontspec}
\setmainfont{Arial}


%\usepackage{fontspec}              % otf шрифты
\usepackage{textpos}                % текстовые блоки
%\usepackage[export]{adjustpage}        % положение картинок 
\usepackage{xcolor}                 % цвет





\begin{document}



\begin{multicols*}{5}

\subsection*{Flush Shutter DC}

\subsection*{Электробезопасность}    %% I SEE THIS (TEXTBF WORKS WELL)
\paragraph{ПАРАГРАФ}                                %% I DONT SEE THIS
\paragraph{PARAGRAPH}                               %% I SEE THIS

text


\end{multicols*}
\end{document}

Answer 2

You are just forgetting to set the sans serif font:

\documentclass{scrartcl}

\usepackage{fontspec}
\usepackage[russian]{babel} % локализация и переносы

% settings
\setmainfont{Arial}
\setsansfont{Arial}

\begin{document}

\textbf{Flush Shutter DC}

\textbf{Электробезопасность}

\paragraph{ПАРАГРАФ}

\paragraph{PARAGRAPH}

text

\end{document}