Weird issue when using \limits

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!