This is usually because of an Exception.
Looking at the PHP Logs
tail -50f /var/log/php-fpm/www-error.log
I found this error:
[11-Jan-2020 04:53:51 UTC] PHP Fatal error: Method Magento\Ui\TemplateEngine\Xhtml\Result::__toString() must not throw an exception, caught TypeError: Argument 2 passed to Magento\Sales\Model\ResourceModel\Order\Shipment\Relation::__construct() must be an instance of Magento\Sales\Model\ResourceModel\Order\Shipment\Track, instance of YYYY\OrderTrackingUpdate\Sales\Model\ResourceModel\Order\Shipment\Track given, called in /var/www/html/vhosts/sharath/XXXXXXXXXX/vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php on line 111 in /var/www/html/vhosts/sharath/XXXXXXXXXX/vendor/magento/module-ui/Component/Wrapper/UiComponent.php on line 0
Turns out, in my case, there was a preference in one of my custom module's
di.xml (that I had overlooked) that was causing the issue.
Once I fixed that - the Order Details pages rendered by just fine.
I hope this helps! :)