Magento 2.1 Product – Fix New Added Products Not Showing

Based on the code I see above, the connection to the database is sitting idle while you iterate over all the emails. My guess is that the code here is taking longer than MySql is configured to wait before closing an idle connection, I.e. The value of the wait_timeout setting which IIRC is 300 (5 min) by default.

Without seeing the exact backtrack of the error, I would assume it's coming after this finishes processing, when the cron dispatcher attempts to update the cron task as complete in the cron_schedule table.

Out of the box, Magento does not attempt to reopen connections MySql has closed and will fail if it's been closed and it tries to use it.

To fix this, you'll either need to up the timeout setting in the mysql stack or ping the database to maintain an open connection.

Ensure the followings as well.

• Your category is under the relevant root category.
• Under the Display Settings tab of category, the Display Mode should set to "Products Only" or "Static blocks and products". (If this is set to "Static block only`", the products will not display for the category.)
• Clear all the cache (including browser cache)
• Ensure all the products (including associate products) have qty > 0
• Make sure product inventory is set to 'Is in stock' => true
• Try this with Magento default theme, If the products are shown in the default theme, then the issue is with your custom theme.