Text selection in PDF is broken

Question

I am working in a big project and I'm using someone elses template. I recently noted something strange about text selection, and it's that the selection text isn't working properly. In the image below there's an example of what I'm saying

The click was pressed at the beggining of the word "El" at the very start of the paragraph and was released after "psicótico", however, not everything in the text was selected. I'm suspecting there is at least one package causing this, because even though I read what the user wrote here. I have generated lots of PDFs with TeX and other tools. I've been able to select text in these effortlessly. I'm using a relatively long list of packages (not sure what every single of them does, it's someone elses template) I'd prefer not to publish unless strictly necessary, just in case someone knows the exact package causing this. The one I suspected the most, microtype wasn't the responsible, as the problem remained after recompiling without loading.

Any sugestions?

EDIT #1: the loaded packages aren't the problem, because I created a new document with all my packages and I was unable to reproduce my problem.

EDIT #2 I am able to reproduce my problem, with the same exact text of the image (however, this problem is present in the whole document) I'm starting to suspect of the "tildes" (á, é, í, ó, ú)

\documentclass[a4paper,10pt,openany]{book}
\usepackage{ifthen}
\usepackage{fancyhdr}
\usepackage{titlesec}
\usepackage[font=small,format=plain,labelfont= sc]{caption}
\usepackage{anysize}
\usepackage{amsfonts,amsmath}
\usepackage[spanish,es-tabla]{babel}
\usepackage[utf8]{inputenc}
\usepackage[usenames, dvipsnames]{color}
\usepackage[hidelinks]{hyperref}
\usepackage{booktabs,multirow}
\usepackage[square,sort,comma,numbers]{natbib}
\usepackage{graphicx}
\usepackage[toc,page]{appendix}
\usepackage{parskip}
\usepackage{microtype}
\usepackage{tikz,bibunits,graphicx,circuitikz}
\usepackage{mathpazo}
\usepackage{enumitem}
\usepackage{filecontents}
\usepackage{pgfplots, pgfplotstable}
    \usepgfplotslibrary{statistics}
    \pgfplotsset{compat=1.9}
\usepackage{makecell}
\usepackage{tablefootnote}
\usepackage{float,placeins}

\begin{document}
El trastorno por déficit de atención e hiperactividad (TDAH) es un trastorno disruptivo del comportamiento que se caracteriza principalmente por la presencia de un patrón persistente de inatención y/o hiperactividad e impulsividad. Para que se considere que la patología esté presente, los síntomas de hiperactividad, impulsividad o falta de atención deben manifestarse desde antes de los siete años de edad, aunque no es estrictamente necesario, debido a que muchos individuos son diagnosticados después de mostrar los síntomas durante varios años después de esta edad. La sintomatología se ha de presentar en la casa, el colegio el trabajo, o al menos en dos de estas tres dependencias, y debe afectar significativamente la operatividad del paciente, bien sea de forma social, académica o laboral. También debe tenerse en cuenta que tales síntomas no deben poder explicarse solo debido a una fase del trastorno pervasivo del comportamiento, la esquizofrenia, o algún otro desorden psicótico.

\end{document}

At least for me, this code reproduces my error.