How to fix the Underfull \vbox badness has occurred while \output is active on my memoir chapter style?

Thanks to @Bernard comment, adding \raggedbottom fixed this warning. While searching it, I found the questions:

1. \flushbottom vs \raggedbottom)
2. Do I have to care about bad boxes?
3. badness messages when changing from report to book class
4. \raggedbottom in book. Is it right way?
5. Restore default \raggedbottom footnote behaviour when using one of the Koma script classes

Also filling that specific page with text fixed the warning. Basically somehow the contents of the page where being pushed to the next page letting a big whole on the original page.

On this version the warning is fixed by filling up text:

% ----------------------------------------------------------
\chapter[Nullam elementum urna vel imperdiet sodales elit ipsum]{Nullam elementum urna vel imperdiet sodales elit ipsum pharetra ligula
    ac pretium ante justo a nulla curabitur tristique arcu eu metus}
% ----------------------------------------------------------

\showfont
\section[Some encoding tests]{\showfont}

1. How to display the font size in use in the final output,
2. How to display the font size in use in the final output,
3. How to display the font size in use in the final output,
4. How to display the font size in use in the final output,
5. How to display the font size in use in the final output,
6. How to display the font size in use in the final output,

7. How to display the font size in use in the final output,
8. How to display the font size in use in the final output,
9. How to display the font size in use in the final output,
10. How to display the font size in use in the final output,
11. How to display the font size in use in the final output,
12. How to display the font size in use in the final output,

\subsection{\showfont}

1. How to display the font size in use in the final output,
2. How to display the font size in use in the final output,
3. How to display the font size in use in the final output,
4. How to display the font size in use in the final output,
5. How to display the font size in use in the final output,
6. How to display the font size in use in the final output,

7. How to display the font size in use in the final output,
8. How to display the font size in use in the final output,
9. How to display the font size in use in the final output,
10. How to display the font size in use in the final output,
11. How to display the font size in use in the final output,
12. How to display the font size in use in the final output,

\subsubsection{\showfont}

1. How to display the font size in use in the final output,
2. How to display the font size in use in the final output,
3. How to display the font size in use in the final output,
4. How to display the font size in use in the final output,
5. How to display the font size in use in the final output,
6. How to display the font size in use in the final output,

7. How to display the font size in use in the final output,
8. How to display the font size in use in the final output,
9. How to display the font size in use in the final output,
10. How to display the font size in use in the final output,
11. How to display the font size in use in the final output,
12. How to display the font size in use in the final output,

\subsubsubsection{\showfont}

1. How to display the font size in use in the final output,
2. How to display the font size in use in the final output,
3. How to display the font size in use in the final output,
4. How to display the font size in use in the final output,
5. How to display the font size in use in the final output,
6. How to display the font size in use in the final output,
7. How to display the font size in use in the final output,

8. How to display the font size in use in the final output,
9. How to display the font size in use in the final output,
10. How to display the font size in use in the final output,
11. How to display the font size in use in the final output,
12. How to display the font size in use in the final output,


Lipsum me [55-57]

I would prefer this alternative over disabling the pages bottom justifications with \raggedbottom. I believe the problem was caused by pilling up empty of sections as showed on question end, which somehow pushed all the empty sections to the next page creating the whole at the first page bottom:

% ----------------------------------------------------------
\chapter[Nullam elementum urna vel imperdiet sodales elit ipsum]{Nullam 
    elementum urna vel imperdiet sodales elit ipsum pharetra ligula
    ac pretium ante justo a nulla curabitur tristique arcu eu metus}
% ----------------------------------------------------------

\showfont
\section[Some encoding tests]{\showfont}
\subsection{\showfont}
\subsubsection{\showfont}
\subsubsubsection{\showfont}

The solution to the above case is to manually insert a \newpage command, on the page which is issuing the warning. On this case the document would be like:

% ----------------------------------------------------------
\chapter[Nullam elementum urna vel imperdiet sodales elit ipsum]{Nullam 
    elementum urna vel imperdiet sodales elit ipsum pharetra ligula
    ac pretium ante justo a nulla curabitur tristique arcu eu metus}
% ----------------------------------------------------------

\showfont
\newpage

\section[Some encoding tests]{\showfont}
\subsection{\showfont}
\subsubsection{\showfont}
\subsubsubsection{\showfont}

Just notice this last example only works if attached to my main document. When this is reproduced alone, no empty page is throw down:

This is probably due some other setting somewhere embedded on my main document class.