After latest translatewiki.net code update: this started appearing in the logs frequently:
[28-Aug-2019 12:49:49 UTC] PHP Fatal error: Uncaught Wikimedia\Rdbms\DBUnexpectedError: Wikimedia\Rdbms\Database::close: mass commit/rollback of peer transaction required (DBO_TRX set) in /srv/mediawiki/tags/2019-08-28_12:42:55/includes/libs/rdbms/database/Database.php:888 Stack trace: #0 /srv/mediawiki/tags/2019-08-28_12:42:55/includes/libs/rdbms/loadbalancer/LoadBalancer.php(1506): Wikimedia\Rdbms\Database->close() #1 /srv/mediawiki/tags/2019-08-28_12:42:55/includes/libs/rdbms/loadbalancer/LoadBalancer.php(2049): Wikimedia\Rdbms\LoadBalancer->Wikimedia\Rdbms\{closure}(Object(Wikimedia\Rdbms\DatabaseMysqli)) #2 /srv/mediawiki/tags/2019-08-28_12:42:55/includes/libs/rdbms/loadbalancer/LoadBalancer.php(1507): Wikimedia\Rdbms\LoadBalancer->forEachOpenConnection(Object(Closure)) #3 /srv/mediawiki/tags/2019-08-28_12:42:55/includes/libs/rdbms/loadbalancer/LoadBalancer.php(1496): Wikimedia\Rdbms\LoadBalancer->closeAll() #4 /srv/mediawiki/tags/2019-08-28_12:42:55/includes/libs/rdbms/lbfactory/LBFactory.php(229): Wikimedia\Rdbms\LoadBalancer->disable() #5 /srv/ in /srv/mediawiki/tags/2019-08-28_12:42:55/includes/libs/rdbms/database/Database.php on line 888
T217819: Wikimedia\\Rdbms\\Database::close: mass commit/rollback of peer transaction required (DBO_TRX set) looks very similar.
At least the error message should be such that there is something to help debugging this.