CakePHP 4 FormProtector instance has not been created error - php

Question

I am currently in the process of updating a (rather big) application from CakePHP 3 to 4.
I have this template:
<?= $this->Form->create(
$dmpLayer,
[
'url' => [
'controller' => 'DmpLayers',
'action' => 'edit',
],
]
); ?>
<div class="row">
<div class="col-4">
<?= $this->element('DataLayers/layer-table'); ?>
</div>
<div id="form-div" class="col-6">
<div class="layer-form">
<?= $this->element('DataLayers/form') ?>
</div>
</div>
<div class="col-2">
<div class="layer-form">
<h2>Form Actions</h2>
<?= $this->Form->submit('Create/Update Layer', ['class' => 'btn btn-success']); ?>
</div>
</div>
</div>
<?= $this->Form->end(); ?>
<?= $this->Html->script('data-layers'); ?>
which includes the DataLayers/form element:
<div class="row">
<div class="col-12">
<h4>Artist Layer</h4>
<?php
echo $this->Html->tag('fieldset', $this->element(
'actions/add',
[
'url' => [
'prefix' => 'Admin',
'plugin' => false,
'controller' => 'SegmentCores',
'action' => 'add',
],
]
)
. $this->Form->control('artist_layer.segment_cores[]', [
'multiple',
'options' => $segmentCores,
'label' => 'Segment Core',
'value' => $selectedValues['segment_cores'],
])
. $this->Form->control('artist_layer.segment_potentials[]', [
'multiple',
'options' => $segmentPotentials,
'label' => 'Segment Potential',
'value' => $selectedValues['segment_potentials'],
])
. $this->Form->control('artist_layer.layer_tags[]', [
'multiple',
'options' => $layerTags,
'label' => 'Artist Tag',
'value' => $selectedValues['artist_tags'],
])
. $this->Form->control('artist_layer.genres[]', [
'empty' => 'No genre set',
'options' => $genres,
'label' => 'Genre',
'value' => $selectedValues['genres'],
]);
?>
</div>
</div>
<?php
$this->Form->unlockField('artist_layer.genres');
$this->Form->unlockField('artist_layer.segment_cores');
$this->Form->unlockField('artist_layer.segment_potentials');
$this->Form->unlockField('artist_layer.layer_tags');
?>
In the initialize function of the AppController I have this:
$this->loadComponent('Security');
When I visit the page, it doesn't render and I immediately get this error:
FormProtector instance has not been created. Ensure you have loaded the FormProtectionComponent in your controller and called FormHelper::create() before calling FormHelper::unlockField()
This is the only form in my application for which this error happens. Every other form is working fine, and I am calling the Form->unlockField() function in many of them.
I am obviously calling Form->create() in my code, so is this because I am including an element to add fields to the form that is defined in the "main" template? Or is there some other explanation?
I have already attempted adding
$this->loadComponent('FormProtection');
to my AppController, but this causes a whole lot more problems in many other places in the app, and it doesn't solve the problem anyway (the page renders, but I get an error when submitting the form to save the data).