Tcolorbox unbroken box prevents next breakable box from breaking

Question

I think I've stumbled upon a tcolorbox bug: whenever there are two consecutive breakable boxes, neither can fit unbroken in the current page, and the content of the first is unbreakable (e.g. an image) while the content of the second is breakable (e.g. text), then the first is moved to the next page as expected, but for some reason, the second one is not broken and end-up overflowing from the page. Making the first box unbreakable (which should change basically nothing since it can not be broken) fixes the problem, which makes me think that this is due to tcolorbox somehow wrongly applying the decision to not break the first box to the second box.

The actual use case is a PhD thesis where every figure, theorem (and fact, proposition, remark, etc.) and proof is in a breakable tcolorbox. This problem happens at unexpected places because the figures float while the theorems do not, which makes manually making some boxes unbreakable unmanageable.

I've looked at the code for the beakable, tried changing the values of booleans \tcb@break@allowedtrue and \tcb@ignorenobreaktrue and placing the box in a group (to prevent value changes from leaking to the other box), but this had no effect.

\documentclass{article}
\usepackage[most]{tcolorbox}
\usepackage{afterpage}
\usepackage{lipsum}

\tcbset{enhanced}

\newcommand{\breakablecontent}{\lipsum[1-12]}
\newcommand{\nonbreakablecontent}{\rule{\columnwidth}{\columnwidth}}

\newcommand{\mytest}[1]{
  \lipsum[1-3]
  \afterpage{
    \begin{tcolorbox}[breakable=true]
      \breakablecontent
    \end{tcolorbox}
  }
  \begin{tcolorbox}[breakable=#1]
    \nonbreakablecontent
  \end{tcolorbox}
}

% Naive Attempt to fix this:
%\makeatletter
%\renewcommand{\mytest}[1]{
%  \lipsum[1-3]
%  \afterpage{
%    \tcb@break@allowedtrue\tcb@ignorenobreaktrue
%    \begingroup
%    \begin{tcolorbox}[breakable=true]
%      \breakablecontent
%    \end{tcolorbox}
%    \endgroup
%    \tcb@break@allowedtrue\tcb@ignorenobreaktrue
%  }
%  \tcb@break@allowedtrue\tcb@ignorenobreaktrue
%  \begin{tcolorbox}[breakable=#1]
%    \nonbreakablecontent
%  \end{tcolorbox}
%}
%\makeatother

\begin{document}

\section{Expected behavior}
\mytest{false}

\clearpage

\section{Unexpected behavior}
\mytest{true}

\end{document}

Answer 1

I think, the problem really is related to \afterpage where you place the first tcolorbox in. Without this, the breakpoints work as expected. I am unsure why you need this. Maybe a workaround could be to place a simple \clearpage right before the following tcolorbox?

MWE:

\documentclass{article}
\usepackage[most]{tcolorbox}
\usepackage{lipsum}

\tcbset{enhanced}

\newcommand{\breakablecontent}{\lipsum[1-12]}
\newcommand{\nonbreakablecontent}{\rule{\columnwidth}{\columnwidth}}

\newcommand{\mytest}[1]{
  \lipsum[1-3]
  \clearpage
  \begin{tcolorbox}[breakable=true]
    \breakablecontent
  \end{tcolorbox}
  \clearpage
  \begin{tcolorbox}[breakable=#1]
    \nonbreakablecontent
  \end{tcolorbox}
}

\begin{document}

\section{Expected behavior}
\mytest{false}

\clearpage

\section{Unexpected behavior}
\mytest{true}

\end{document}

Answer 2

Using the magazine library as suggested by Ulrike Fischer fixes the overflow problem but the unbreakable content is inexplicably shifted downwards, outside of its box. Using floats instead of afterpage works.

\documentclass{article}
\usepackage[most]{tcolorbox}
\usepackage{afterpage}
\usepackage{lipsum}

\tcbset{enhanced}

\newcommand{\breakablecontent}{\lipsum[1-12]}
\newcommand{\nonbreakablecontent}{\rule{\columnwidth}{\columnwidth}}

\newboxarray{a}

% Does not work weirdly
\newcommand{\mytest}[1]{
  \lipsum[1-3]\\
  \begin{tcolorbox}[breakable=true, reset and store to box array=a]
    \breakablecontent
  \end{tcolorbox}
  \afterpage{
    \consumeboxarray[a]{1}{}
    \consumeboxarray[a]{2}{}
    \consumeboxarray[a]{3}{}
  }
  \begin{tcolorbox}[breakable=#1]
    \nonbreakablecontent
  \end{tcolorbox}
}

% Works
\renewcommand{\mytest}[1]{
  \lipsum[1-3]\\
  \begin{tcolorbox}[breakable=true, reset and store to box array=a]
    \breakablecontent
  \end{tcolorbox}
  \begin{figure}[p]\consumeboxarray[a]{1}{}\end{figure}
  \begin{figure}[p]\consumeboxarray[a]{2}{}\end{figure}
  \begin{figure}[p]\consumeboxarray[a]{3}{}\end{figure}
  \begin{tcolorbox}[breakable=#1]
    \nonbreakablecontent
  \end{tcolorbox}
}

\begin{document}

\section{Expected behavior}
\mytest{false}

\clearpage

\section{Unexpected behavior}
\mytest{true}

\end{document}