diff --git a/amoro-ams/src/main/java/org/apache/amoro/server/DefaultOptimizingService.java b/amoro-ams/src/main/java/org/apache/amoro/server/DefaultOptimizingService.java
index eb943e6057..3b59004dc8 100644
--- a/amoro-ams/src/main/java/org/apache/amoro/server/DefaultOptimizingService.java
+++ b/amoro-ams/src/main/java/org/apache/amoro/server/DefaultOptimizingService.java
@@ -1081,8 +1081,11 @@ protected void processTask(OptimizerGroupKeepingTask keepingTask) {
               .setProperties(resourceGroup.getProperties())
               .setThreadCount(requiredCores)
               .build();
-      ResourceContainer rc = Containers.get(resource.getContainerName());
       try {
+        // Containers.get throws for an unknown container name; it must stay inside the try so
+        // the finally-block keepInTouch still re-queues the group - otherwise a single lookup
+        // failure silently removes the group from scale-out monitoring until restart.
+        ResourceContainer rc = Containers.get(resource.getContainerName());
         ((AbstractOptimizerContainer) rc).requestResource(resource);
         optimizerManager.createResource(resource);
       } finally {
diff --git a/amoro-ams/src/main/java/org/apache/amoro/server/resource/OptimizerInstance.java b/amoro-ams/src/main/java/org/apache/amoro/server/resource/OptimizerInstance.java
index 0130704d47..70dfcaccdf 100644
--- a/amoro-ams/src/main/java/org/apache/amoro/server/resource/OptimizerInstance.java
+++ b/amoro-ams/src/main/java/org/apache/amoro/server/resource/OptimizerInstance.java
@@ -28,7 +28,9 @@ public class OptimizerInstance extends Resource {
 
   private String token;
   private long startTime;
-  private long touchTime;
+  // Written by thrift heartbeat threads (touch) and read by the keeper thread for expiry
+  // detection without a shared lock; volatile guarantees the keeper observes fresh heartbeats.
+  private volatile long touchTime;
 
   public OptimizerInstance() {}
 
diff --git a/amoro-ams/src/test/java/org/apache/amoro/server/TestOptimizerGroupKeeper.java b/amoro-ams/src/test/java/org/apache/amoro/server/TestOptimizerGroupKeeper.java
index 6e0591d18f..1a820190b9 100644
--- a/amoro-ams/src/test/java/org/apache/amoro/server/TestOptimizerGroupKeeper.java
+++ b/amoro-ams/src/test/java/org/apache/amoro/server/TestOptimizerGroupKeeper.java
@@ -276,6 +276,37 @@ public void testMinParallelismResetToZeroWhenNoResource() throws InterruptedExce
             + ":min-parallelism should be reset to 0 when no resources available and no optimizer exists");
   }
 
+  @Test
+  public void testUnknownContainerKeepsGroupWatchedAndResetsMinParallelism()
+      throws InterruptedException {
+    // Containers.get throws for an unknown container name. The lookup used to sit outside the
+    // try/finally, so the exception skipped keepInTouch and silently removed the group from
+    // scale-out monitoring forever. The keeper must keep watching and eventually reset
+    // min-parallelism like any other permanently-failing scale-out.
+    scaleOutCallCount.set(0);
+    String groupName = TEST_GROUP_NAME + "-7";
+    this.currentGroupName = groupName;
+    Map<String, String> properties = Maps.newHashMap();
+    properties.put(OptimizerProperties.OPTIMIZER_GROUP_MIN_PARALLELISM, "2");
+    properties.put("memory", "1024");
+    ResourceGroup resourceGroup =
+        new ResourceGroup.Builder(groupName, "unknown-container-x")
+            .addProperties(properties)
+            .build();
+
+    optimizerManager().createResourceGroup(resourceGroup);
+    optimizingService().createResourceGroup(resourceGroup);
+
+    Thread.sleep(300);
+
+    ResourceGroup updatedGroup = optimizerManager().getResourceGroup(groupName);
+    Assertions.assertEquals(
+        "0",
+        updatedGroup.getProperties().get(OptimizerProperties.OPTIMIZER_GROUP_MIN_PARALLELISM),
+        groupName
+            + ":keeper must keep watching an unknown-container group and reset min-parallelism");
+  }
+
   /**
    * Test scenario 4: When no resources but has optimizer, min-parallelism will be reset to
    * optimizer's executionParallel.