For some reason, the catalog_product index could not be indexed through the magento scheduler but you are able to reindex it manually and this causes error in loading the product detail page.
This issue has been occurring ever since I upgraded to Magento 2.4.6 and using Smile Elastic Plugin.
{main} {"exception":"[object] (LogicException(code: 0): catalog_product index does not exist yet. Make sure everything is reindexed. at /vendor/smile/elasticsuite/src/module-elasticsuite-core/Index/IndexOperation.php:118)"} []
[2023-07-27T03:33:09.723085+00:00] main.CRITICAL: LogicException: catalog_product index does not exist yet. Make sure everything is reindexed.
The quick workaround is to manually reindex through the CLI which temporarily solve the issue.