[Transform][CI] add debug logging to find the cause of #88991 (#89080)

add debug logging to find the cause of #88991

x-pack/plugin/src/yamlRestTest/resources/rest-api-spec/test/transform/transforms_start_stop.yml

@@ -61,6 +61,15 @@ setup:
               }
             }
           }
+  - do:
+      cluster.put_settings:
+        body: >
+          {
+            "persistent": {
+              "logger.org.elasticsearch.xpack.transform.action": "DEBUG"
+            }
+          }
+
 
 ---
 teardown:
@@ -91,6 +100,15 @@ teardown:
   - do:
       transform.delete_transform:
         transform_id: "airline-transform-start-stop-continuous"
+  - do:
+      cluster.put_settings:
+        body: >
+          {
+            "persistent": {
+              "logger.org.elasticsearch.xpack.transform.action": "INFO"
+            }
+          }
+
 ---
 "Test start transform":
   - do:

x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/action/TransportStopTransformAction.java

@@ -295,6 +295,12 @@ public class TransportStopTransformAction extends TransportTasksAction<Transform
             // If there were failures attempting to stop the tasks, we don't know if they will actually stop.
             // It is better to respond to the user now than allow for the persistent task waiting to timeout
             if (response.getTaskFailures().isEmpty() == false || response.getNodeFailures().isEmpty() == false) {
+                logger.debug(
+                    "[{}] Failure when waiting for transform to stop, task failures: [{}], node failures: [{}]",
+                    request.getId(),
+                    response.getTaskFailures(),
+                    response.getNodeFailures()
+                );
                 RestStatus status = firstNotOKStatus(response.getTaskFailures(), response.getNodeFailures());
                 listener.onFailure(buildException(response.getTaskFailures(), response.getNodeFailures(), status));
                 return;