Weird issue when using \limits

Question

I am writing a summary of my lecture notes when the command \limits acted very strangely: it wrote the bounds below and above but also acted like the \newpage command.

Those are the document characteristics, I use an A4 paper in landscape with 3 columns.
Additionally I wrote a special environment for leftbar.

\documentclass[a4paper,landscape]{report}
\usepackage[a4paper,margin=0.5cm,landscape]{geometry}
\usepackage{amscd}
\usepackage{amsmath}
\usepackage{amsfonts, verbatim, enumerate}
\usepackage{amsthm}
\usepackage{array}
\usepackage{blindtext}
\usepackage{enumitem}
\usepackage{float}
\usepackage{framed}
\usepackage{graphicx}
\usepackage{harvard}
\usepackage{latexsym}
\usepackage{longtable}
\usepackage{makeidx}
\usepackage{multicol}
\usepackage{subfig}
\usepackage{showidx}
\usepackage[light,english,all]{draftcopy}
\renewenvironment{leftbar}{%
    \OuterFrameSep=0ex plus .8ex
    \def\FrameCommand{{\vrule width 1pt}\hspace{3pt}}%
    \MakeFramed {\advance\hsize-\width \FrameRestore}
    \noindent\ignorespaces
    }{%
    \endMakeFramed
    \csname@endparenv\endcsname
}
\begin{document}
\begin{multicols}{3}

I enclose herewith the screenshots showing the problem.
Here the code before:

And after (the issue is at the cursor):

And that is what happened to the pdf.
Before:

After:

Does anyone know what this is due to?

Many thanks in advice for your answers!