Api4 related error with Firewall: Cleanup job

I've got the following error report happening daily, from this cron:

Cron ubuntu@www /usr/local/bin/cv api job.execute --user=[username] --cwd=/var/www/acreresidency.org/web/sites/default/files/civicrm >/dev/null

Here's the log:

Recoverable fatal error: Object of class Civi\Api4\Generic\Result could not be converted to string in /var/www/acreresidency.org/vendor/civicrm/civicrm-core/CRM/Core/JobManager.php on line 273 #0 /var/www/acreresidency.org/web/core/includes/bootstrap.inc(600): _drupal_error_handler_real(4096, 'Object of class...', '/var/www/acrere...', 273, Array)
#1 /var/www/acreresidency.org/vendor/civicrm/civicrm-core/CRM/Core/JobManager.php(273): _drupal_error_handler(4096, 'Object of class...', '/var/www/acrere...', 273, Array)
#2 /var/www/acreresidency.org/vendor/civicrm/civicrm-core/CRM/Core/JobManager.php(140): CRM_Core_JobManager->_apiResultToMessage(Array)
#3 /var/www/acreresidency.org/vendor/civicrm/civicrm-core/CRM/Core/JobManager.php(66): CRM_Core_JobManager->executeJob(Object(CRM_Core_ScheduledJob))
#4 /var/www/acreresidency.org/vendor/civicrm/civicrm-core/api/v3/Job.php(118): CRM_Core_JobManager->execute(false)
#5 /var/www/acreresidency.org/vendor/civicrm/civicrm-core/Civi/API/Provider/MagicFunctionProvider.php(89): civicrm_api3_job_execute(Array)
#6 /var/www/acreresidency.org/vendor/civicrm/civicrm-core/Civi/API/Kernel.php(150): Civi\API\Provider\MagicFunctionProvider->invoke(Array)
#7 /var/www/acreresidency.org/vendor/civicrm/civicrm-core/Civi/API/Kernel.php(81): Civi\API\Kernel->runRequest(Array)
#8 /var/www/acreresidency.org/vendor/civicrm/civicrm-core/api/api.php(22): Civi\API\Kernel->runSafe('job', 'execute', Array)
#9 phar:///usr/local/bin/cv/src/Command/ApiCommand.php(53): civicrm_api('job', 'execute', Array)
#10 phar:///usr/local/bin/cv/vendor/symfony/console/Command/Command.php(257): Civi\Cv\Command\ApiCommand->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#11 phar:///usr/local/bin/cv/vendor/symfony/console/Application.php(850): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#12 phar:///usr/local/bin/cv/vendor/symfony/console/Application.php(193): Symfony\Component\Console\Application->doRunCommand(Object(Civi\Cv\Command\ApiCommand), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#13 phar:///usr/local/bin/cv/src/Application.php(48): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#14 phar:///usr/local/bin/cv/vendor/symfony/console/Application.php(124): Civi\Cv\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#15 phar:///usr/local/bin/cv/src/Application.php(17): Symfony\Component\Console\Application->run()
#16 phar:///usr/local/bin/cv/bin/cv(26): Civi\Cv\Application::main('phar:///usr/loc...')
#17 /usr/local/bin/cv(10): require('phar:///usr/loc...')
#18 {main}

There's nothing there to indicate it's from Firewall, but when I look at my scheduled jobs listing, "Firewall: Cleanup" is the only one with a timestamp that matches up with this error. Also, I started getting the log after enabling the firewall module.

I'm using CiviCRM 5.24.2 on Drupal 8.8.5 with PHP 7.2.24.