Mrthdrb

In catalog_product_view.xml I have the following section:

<referenceBlock name="product.info.details">
 <block class="MagentoFrameworkViewElementTemplate" template="Magento_Catalog::product/tabs/tab1.phtml" name="extra-tab-1" group="detailed_info">
 <arguments>
 <argument name="title" translate="true" xsi:type="string">Extra Tab 1</argument>
 </arguments>
 </block>
 <block class="MagentoFrameworkViewElementTemplate" template="Magento_Catalog::product/tabs/tab2.phtml" name="extra-tab-2" group="detailed_info">
 <arguments>
 <argument name="title" translate="true" xsi:type="string">Extra Tab 2</argument>
 </arguments>
 </block>
</referenceBlock>

My issue is that only "Extra Tab 2" shows up on the product page. If I remove that block and clear caches, "Extra Tab 1" is then displayed.

I was hoping someone had experienced a similar issue and could point me towards a cause. There are no other custom modules or themes interfering with the product page layout.

Have you modified the details.phtml file? If not the only reason I've ever seen the tabs fail to render without any sort of syntax error is when there is no value returned by a tab. For instance if you use a custom attribute, like manufacturer_country in one of the tabs and $product->getManufacturerCountry() returns null or "".

Let's look at the file responsible for rendering the tabs vendor/magento/module-catalog/view/frontend/templates/product/view/details.phtml.

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

// @codingStandardsIgnoreFile

?>
<?php if ($detailedInfoGroup = $block->getGroupChildNames('detailed_info', 'getChildHtml')):?>
 <div class="product info detailed">
 <?php $layout = $block->getLayout(); ?>
 <div class="product data items" data-mage-init='"tabs":"openedState":"active"'>
 <?php foreach ($detailedInfoGroup as $name):?>
 <?php
 $html = $layout->renderElement($name);
 if (!trim($html)) 
 continue;
 
 $alias = $layout->getElementAlias($name);
 $label = $block->getChildData($alias, 'title');
 ?>
 <div class="data item title"
 aria-labeledby="tab-label-<?= /* @escapeNotVerified */ $alias ?>-title"
 data-role="collapsible" id="tab-label-<?= /* @escapeNotVerified */ $alias ?>">
 <a class="data switch"
 tabindex="-1"
 data-toggle="switch"
 href="#<?= /* @escapeNotVerified */ $alias ?>"
 id="tab-label-<?= /* @escapeNotVerified */ $alias ?>-title">
 <?= /* @escapeNotVerified */ $label ?>
 </a>
 </div>
 <div class="data item content" id="<?= /* @escapeNotVerified */ $alias ?>" data-role="content">
 <?= /* @escapeNotVerified */ $html ?>
 </div>
 <?php endforeach;?>
 </div>
 </div>
<?php endif; ?>

These few lines below are what will decide if a tab is rendered or not:

$html = $layout->renderElement($name);
 if (!trim($html)) 
 continue;
 

So unless the value you're trying to return is empty or you've customized details.phtml then there is no reason for the tab not to be rendered.

I just stumbled across the answer.

As of Magento 2.3.1, if the tab does not have a sort order set, it uses 0. Unfortunately, Magento uses that sort order as the array key, so if multiple tabs do not have a sort order set, they overwrite the same array element and only the last tab is left. This issue is not present in 2.3.0.

The solution is to simply ensure that each tab has a sort order set, e.g.:

<argument name="sort_order" xsi:type="string">30</argument>