Nuxt and Netlify Form File Upload Problem - forms

Question

in a Nuxt site I have a form with a field of type "file", and a Name, Email and Message fields.
Name, Email and Message are working flawlessy everytime, instead the "file" field ONLY WORKS when the first page visited is the page where the form is (or it's reloaded). If a user, let's say, land on the homepage and only then reach the form page, the message sent from the form will not contain the file that was attached.
What can cause this? I've already tried to reset the form on the mounted hook, or reset only the "file" field but with no luck.
This is the form component code "TheFormJob.vue":
<template>
<div>
<form name="job" netlify-honeypot="bot-field" method="post" action="/success" data-netlify="true">
<input type="hidden" name="form-name" value="job" >
<p class="hidden">
<label>Don’t fill this out: <input name="bot-field"></label>
</p>
<div class="form">
<div class="form__name">
<input class="form__field" name="name" id="name" :placeholder="$t('contatti.nomeForm')" required >
</div>
<div class="form__email">
<input class="form__field" type="email" name="email" id="email" placeholder="Email*" required >
</div>
<div class="form__upload">
<input class="form__field" type="file" name="fileToUpload" id="fileToUpload" accept=".doc, .docx, .pdf" required>
</div>
<div class="form__textarea">
<textarea class="form__field" name="message" id="message" :placeholder="$t('contatti.messaggioForm')" required></textarea>
</div>
<div class="form__privacy extra-mt">
<label><input type="checkbox" name="privacy" required> {{$t('contatti.privacy')}}</label>
</div>
<div class="form__send extra-mt">
<button class="default-button" type="submit" value="Invia" >{{$t('contatti.invia')}} </button>
</div>
</div>
</form>
</div>
</template>
<script>
export default {
mounted(){
const dis = this
const uploadField = document.getElementById("fileToUpload");
uploadField.onchange = function() {
if(this.files[0].size > 1048576){ // 1MB
alert(dis.$t('lavora.fileAlert'));
}
}
}
}
</script>
In the page "index.vue":
<template>
<div>
<div class="container">
<div class="first row extra-mt5-md is-center">
<div class="col-12 col-4-md text-center" style="padding: 2rem 0">
<h1>{{$t('lavora.title')}}</h1>
</div>
</div>
<div class="second row">
<div class="col-12 col-4-md image" />
<div class="col-12 col-8-md content">
<p>{{$t('lavora.p1')}}</p>
<TheFormJob class="extra-mt5" />
</div>
</div>
<div class="third row">
<div class="col-12">
<nuxt-link class="default-button-full" :to="localePath('contatti')">{{$t('contatti.title')}} → </nuxt-link>
</div>
</div>
</div>
</div>
</template>