database_logger logs a log entry for removed log entries per cron job

+++ b/src/Plugin/ultimate_cron/Logger/DatabaseLogger.php
@@ -93,6 +94,12 @@ class DatabaseLogger extends LoggerBase implements PluginCleanupInterface, Conta
+    if ($counter > 0) {
+      \Drupal::logger('database_logger')->info('@count log entries removed for job @name', array(
+        '@count' => $counter,
+        '@name' => $job->id(),
+      ));
+    }

not for job @name, but "for @count jobs". you're outside of the loop here, this will simply only report it for the last job.

you need to count deleted messages together and also count the jobs for which messages were deleted but only if ther was at least one.

+++ b/src/Plugin/ultimate_cron/Logger/DatabaseLogger.php
@@ -85,13 +87,20 @@ class DatabaseLogger extends LoggerBase implements PluginCleanupInterface, Conta
         // Get the plugin through the job so it has the right configuration.
-        $job->getPlugin('logger')->cleanupJob($job);
+        $job_count++;
+        $counter = $job->getPlugin('logger')->cleanupJob($job);
         $class = \Drupal::entityTypeManager()->getDefinition('ultimate_cron_job')->getClass();

counter is just the count of the last job. you need to sum them together. and as I wrote, only count jobs for which you actually delete messages:

if ($counter) {
$counters[$job->id()] = $counter;
}

For example like that, then you can use count() and array_sum()

Yes, I think this is correct now. Tests would be nice but seems to be pretty complex to add useful tests.

Feel free to re-open and set to 7.x. But plently of similar 7.x issues have been closed with the suggestion to use some watchdog filter module. I don't maintain that version.