diff --git a/Directory.Packages.props b/Directory.Packages.props
index 25c51077a..6f8957b14 100644
--- a/Directory.Packages.props
+++ b/Directory.Packages.props
@@ -7,7 +7,7 @@
     <AkkaPersistenceSqlHostingVersion>1.5.70</AkkaPersistenceSqlHostingVersion>
     <AkkaRemindersVersion>0.7.0</AkkaRemindersVersion>
     <OpenTelemetryVersion>1.17.0</OpenTelemetryVersion>
-    <SlackNetVersion>0.17.10</SlackNetVersion>
+    <SlackNetVersion>0.17.11</SlackNetVersion>
     <DiscordNetVersion>3.20.1</DiscordNetVersion>
     <MattermostNetVersion>5.0.7</MattermostNetVersion>
     <MicrosoftExtensionsAIVersion>10.8.3</MicrosoftExtensionsAIVersion>
diff --git a/src/Netclaw.Actors.Tests/Reminders/ReminderManagerActorTests.cs b/src/Netclaw.Actors.Tests/Reminders/ReminderManagerActorTests.cs
index 5561049f7..2faf0c321 100644
--- a/src/Netclaw.Actors.Tests/Reminders/ReminderManagerActorTests.cs
+++ b/src/Netclaw.Actors.Tests/Reminders/ReminderManagerActorTests.cs
@@ -604,9 +604,18 @@ await manager.Ask<ReminderHealthResponse>(
             TimeSpan.FromSeconds(30),
             TestContext.Current.CancellationToken);
 
-        Assert.Contains(sink.Alerts, alert =>
-            alert.Category == AlertType.ReminderSchemaDropped
-            && alert.Summary.Contains(reminderId, StringComparison.Ordinal));
+        // Keep the Ask as the startup barrier (it absorbs dispatcher
+        // scheduling latency under parallel CI load), but poll the sink
+        // instead of trusting a one-shot post-Ask read: the health reply
+        // proves PreStart completed, not that the alert reached the sink.
+        // This test has flaked on CI twice (#1405, #1844) with an empty
+        // sink immediately after a successful Ask reply.
+        await AwaitAssertAsync(() =>
+        {
+            Assert.Contains(sink.Alerts, alert =>
+                alert.Category == AlertType.ReminderSchemaDropped
+                && alert.Summary.Contains(reminderId, StringComparison.Ordinal));
+        }, duration: TimeSpan.FromSeconds(30), cancellationToken: TestContext.Current.CancellationToken);
     }
 
     /// <summary>