Empty TinyMCE in Custom Metabox in Firefox

We use the TinyMCE Editor in custom metaboxes to allow our authors to enter additional text, which we then display in various sections of the portal. As an example, a summary for a test report.

In Firefox, we are now facing an issue where the editor’s frame (icons/controls) loads, but the iframe itself remains empty. The content to be displayed is present in the textarea but cannot be shown. No such Problems in Chrome, Edge or Safari.

The problem is not persistent but occurs in approximately 80% of backend requests.

The call for the editor:

$data = $data[0]['short_conclusion'];
wp_nonce_field($this->nonceAction, $this->nonceName); ?>
<div>
    <h3>Kurzfazit</h3>
    <?php wp_editor(htmlspecialchars_decode($data), 'iim_producttest_short_conclusion_editor', $settings = array('textarea_name'=>'iim_producttest_short_conclusion_editor', 'media_buttons' => false, 'textarea_rows' => 5, 'wpautop' => false, 'quicktags' => false, 'tinymce' => $tinymcsCallback)) ?>
</div>

I suspect a loading order issue, but I can’t find any approach for analysis or the actual cause. Can anyone help?