From
// Check if the product belongs to category flash deal
$allCategoryIds = $product->getCategoryIds();
/** @var \Magento\Catalog\Model\ResourceModel\Category\Collection $categoryCollection */
$categoryCollection = $this->_categoryCollection->create();
$categoryCollection->addFieldToFilter('entity_id', ['in' => $allCategoryIds]);
/** @var \Magento\Catalog\Model\Category[] $categories */
$categories = $categoryCollection->getItems();
foreach ($categories as $category) {
	$categoryIds = $category->getParentIds();
	$allCategoryIds = array_merge($allCategoryIds, $categoryIds);
}
$allCategoryIds = array_unique($allCategoryIds);
if (in_array($value, $allCategoryIds)) {
	$canShow = true;
}

To
// Check if the product belongs to category flash deal
$categories = $product->getCategoryCollection();
$allCategoryIds = [];
foreach ($categories as $category) {
	$allCategoryIds = array_merge($allCategoryIds, explode('/', $category->getPath()));
}
if (in_array($value, $allCategoryIds)) {
	$canShow = true;
}