It looks like the error is:

[2017-07-10 07:06:11] request.CRITICAL: Uncaught PHP Exception Doctrine\DBAL\Exception\DriverException: "An exception occured in driver: SQLSTATE[HY000] [2003] Can't connect to MySQL server on '127.0.0.1' (111)" at /var/www/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php line 115 {"exception":"[object] (Doctrine\\DBAL\\Exception\\DriverException(code: 0): An exception occured in driver: SQLSTATE[HY000] [2003] Can't connect to MySQL server on '127.0.0.1' (111) at /var/www/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php:115, Doctrine\\DBAL\\Driver\\PDOException(code: 2003): SQLSTATE[HY000] [2003] Can't connect to MySQL server on '127.0.0.1' (111) at /var/www/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOConnection.php:47, PDOException(code: 2003): SQLSTATE[HY000] [2003] Can't connect to MySQL server on '127.0.0.1' (111) at /var/www/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOConnection.php:43)"} []

This is because it's not yet set up with its own database for recording hits, and is still pointing to a non-existant localhost MySQL server.

@MusikAnimal I think you were working on this? Something about having separate databases for new and old xtools? Maybe you already fixed it (probably!) and Composer clobbered the DB config at some point? (Sorry! Probably my fault, if it did.)

In T170100#3419431, @Samwilson wrote:

This is because it's not yet set up with its own database for recording hits, and is still pointing to a non-existant localhost MySQL server.

@MusikAnimal I think you were working on this? Something about having separate databases for new and old xtools? Maybe you already fixed it (probably!) and Composer clobbered the DB config at some point? (Sorry! Probably my fault, if it did.)

Yep. I haven't gotten around to fixing it because we're going to change prod servers soon. For more on that see T169590#3422038

Okay, new prod server is recording hits correctly now: https://xtools.wmflabs.org/meta