minipage messes up spacings

Question

I have some troubles with spacing when using minipages to keep some content together.

\documentclass[a4paper,10pt,notitlepage]{article}
\usepackage{geometry} 
\geometry{
    a4paper,
    head=20mm,
    left=20mm,
    right=10mm,
    top=25mm,
    bottom=25mm,
    foot=8mm
}
\usepackage[default,scale=0.95]{opensans} %Schriftart FEHLER
\usepackage{tabularx}
\usepackage{booktabs}                       % use package booktabs for easy creating tables
\usepackage{caption}
\usepackage{subcaption} 
\usepackage[table]{xcolor}
\usepackage{setspace}   
\usepackage{floatflt,epsfig} 
\usepackage{blindtext}
\usepackage[flushleft]{threeparttable}      % to have a dedicated notes section after tables
\usepackage{titlesec}

\setlength{\fboxsep}{0pt}%
\setlength{\fboxrule}{1pt}%
\setlength{\abovecaptionskip}{7pt}
\setlength{\belowcaptionskip}{7pt}
\setlength{\textfloatsep}{10pt}

\linespread{1.0}   
\setlength{\parindent}{0pt}                 % verhindert Absatzeinrueckung nach Bildern

\usepackage[framemethod=tikz]{mdframed}

% CAPTION STYLE
\DeclareCaptionFormat{labelstyle}{% <- needed
\setlength\fboxsep{3pt}% <- needed
\colorbox{blue}{{#1}}#2#3%
} 
\definecolor{blue}{HTML}{336699}
\captionsetup[table]{singlelinecheck=false, labelfont={color=white}}    % Rechtsbündige Tabellen und Bildbeschreibung
\captionsetup[figure]{format=labelstyle, labelfont={color=white}, 
justification=raggedright,% <- only needed if longer captions should not be justified
singlelinecheck=false% <- added
}

% SECTION STYLE
% -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\titleformat{\section}
{\Large\bfseries\color{blue}}
{\thesection}{1em}{} %\titleformat{\section}{\Large\bfseries\color{blue}}{\thesection}{1em-Abstand}
\titleformat{\subsection}
{\large\bfseries\color{blue}}
{\thesubsection}{1em}{} %\titleformat{\section}{\Large\bfseries\color{blue}}{\thesection}{1em-Abstand}
\titleformat{\subsubsection}
{\bfseries\color{blue}}
{\thesubsubsection}{1em}{} %\titleformat{\section}{\Large\bfseries\color{blue}}{\thesection}{1em-Abstand}
% -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------


\newcommand{\astroltable} { 
    \captionsetup{type=table, format=labelstyle}
    \arrayrulecolor{blue} 
    % \aboverulesep = 0mm 
    % \belowrulesep = 0mm 
    }

    \newenvironment{tableenv}[2]{
        \everypar{}
        \def\tablecaption{#1}
        \def\tablelabel{tab:#2}
        \begin{center}
            \begin{footnotesize} 
                \astroltable
                \begin{threeparttable}
    }{
            \end{threeparttable}
            \caption{\tablecaption}
            \label{\tablelabel}
        \end{footnotesize}
    \end{center}}

\begin{document}

\section{A section}
\begin{minipage}{\textwidth}
    \subsection{A subsection}
    \blindtext
    \begin{tableenv}{blubb}{blubb}
        \begin{tabularx}{\textwidth}{p{0.2\textwidth}p{0.25\textwidth}Xp{0.075\textwidth}p{0.075\textwidth}p{0.075\textwidth}p{0.075\textwidth}}
            \toprule
            \textbf{City}  & \textbf{Country} & \textbf{min.} & \textbf{typ.} & \textbf{max.} & \textbf{Rate} \\ \midrule
            New York             & US and A               & -             & 1.0             & -            & n/a            \\ \bottomrule
        \end{tabularx}
    \end{tableenv}
\end{minipage}

\strut
\blindtext
\begin{tableenv}{blubb2}{blubb2}
    \begin{tabularx}{\textwidth}{p{0.2\textwidth}p{0.25\textwidth}Xp{0.075\textwidth}p{0.075\textwidth}p{0.075\textwidth}p{0.075\textwidth}}
        \toprule
        \textbf{City}  & \textbf{Country} & \textbf{min.} & \textbf{typ.} & \textbf{max.} & \textbf{Rate} \\ \midrule
        New York             & US and A               & -             & 1.0             & -            & n/a            \\ \bottomrule
    \end{tabularx}
\end{tableenv}
\blindtext

\end{document}

One problem is the missing space above Table 1, this is introduced with the use of the titlesec package and seems to be caused if the minipage starts with a sectiontitle. Is there a way to correct this?
The other problem is the space between the caption of Table 1 and the following text which is different from Table 2.

Answer 1

I don't think that the issues you've encountered are all that closely related to the use of a minipage environment. Instead, I would argue, the issues appear to be related to shortcomings in the definitions of the \astroltable macro and the tableenv environment. The fact that you define the tabularx environments to contain 7 columns, but then only use 6 columns, doesn't exactly help either.

Does the layout shown in the following screenshot come closer to meeting your objectives?

\documentclass[a4paper,10pt,notitlepage]{article}

\usepackage{geometry}
\geometry{a4paper,
    head=20mm,foot=8mm,
    left=20mm,right=10mm,
    top=25mm,bottom=25mm,
}

\usepackage[default,scale=0.95]{opensans}

\usepackage{tabularx,booktabs} 
\usepackage{caption,subcaption}
% CAPTION STYLE
\DeclareCaptionFormat{labelstyle}{% 
    \setlength\fboxsep{3pt}%
    \colorbox{myblue}{{#1}}#2#3}
\captionsetup[table]{singlelinecheck=false,
    labelfont={color=white}}
\captionsetup[figure]{format=labelstyle,
    labelfont={color=white},
    justification=raggedright,
    singlelinecheck=false}


\usepackage{titlesec}
% SECTION STYLE
\titleformat{\section}{%
    \Large\bfseries\color{myblue}}{\thesection}{1em}{}
\titleformat{\subsection}{%
    \large\bfseries\color{myblue}}{\thesubsection}{1em}{}
\titleformat{\subsubsection}{%
    \bfseries\color{myblue}}{\thesubsubsection}{1em}{}


\usepackage[table]{xcolor}
\definecolor{myblue}{HTML}{336699}

\usepackage{setspace}
%%%%\linespread{1.0} % better: "\singlespacing"

%%%%\usepackage{floatflt,epsfig}  % shouldn't be needed

\usepackage{blindtext}
\usepackage[flushleft]{threeparttable}   
\usepackage[framemethod=tikz]{mdframed}

\setlength{\fboxsep}{0pt}%
\setlength{\fboxrule}{1pt}%

\setlength{\abovecaptionskip}{7pt}
\setlength{\belowcaptionskip}{10pt}
\setlength{\textfloatsep}{10pt}

\setlength{\parindent}{0pt} 

\newcommand{\astroltable}{%
    \captionsetup{type=table, format=labelstyle,
        skip=0.75\baselineskip} % <-- new (default is 1\baselineskip)
    \arrayrulecolor{myblue}}

\newenvironment{tableenv}[2]{% quite a few changes here
    \par\medskip
    \def\tablecaption{#1}
    \def\tablelabel{tab:#2}
    \footnotesize % \footnotesize is a macro, not an environment
    \astroltable
    \begin{threeparttable}
    }{%
    \caption{\tablecaption}
    \label{\tablelabel}
    \end{threeparttable} % place this *after* \caption and \label
    }

\begin{document}

\section{A section}
\subsection{A subsection}
\begin{minipage}{\textwidth}
    \blindtext
    \begin{tableenv}{blubb}{blubb}
    \begin{tabularx}{\textwidth}{%
         p{0.2\textwidth} p{0.3\textwidth} *{4}{X}}
    \toprule
    \textbf{City} & \textbf{Country} & 
    \textbf{min.} & \textbf{typ.} & 
    \textbf{max.} & \textbf{Rate} \\
    \midrule
    New York & US and A & -- & 1.0 & -- & n/a \\ 
    \bottomrule
    \end{tabularx}
    \end{tableenv}
\end{minipage}

    \blindtext
    \begin{tableenv}{blubb2}{blubb2}
    \begin{tabularx}{\textwidth}{%
         p{0.2\textwidth} p{0.3\textwidth} *{4}{X}}
    \toprule
    \textbf{City} & \textbf{Country} & 
    \textbf{min.} & \textbf{typ.} & 
    \textbf{max.} & \textbf{Rate} \\
    \midrule
    New York & US and A & -- & 1.0 & -- & n/a \\ 
    \bottomrule
    \end{tabularx}
    \end{tableenv}

    \blindtext
\end{document}