diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
index 14a1a089713..193bd766f3d 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
@@ -1236,12 +1236,12 @@ static void glb_notify_on_state_change_locked(grpc_lb_policy* pol,
 static void lb_call_on_retry_timer_locked(void* arg, grpc_error* error) {
   glb_lb_policy* glb_policy = (glb_lb_policy*)arg;
   glb_policy->retry_timer_active = false;
-  if (!glb_policy->shutting_down && error == GRPC_ERROR_NONE) {
+  if (!glb_policy->shutting_down && glb_policy->lb_call == NULL &&
+      error == GRPC_ERROR_NONE) {
     if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
       gpr_log(GPR_INFO, "Restaring call to LB server (grpclb %p)",
               (void*)glb_policy);
     }
-    GPR_ASSERT(glb_policy->lb_call == NULL);
     query_for_backends_locked(glb_policy);
   }
   GRPC_LB_POLICY_WEAK_UNREF(&glb_policy->base, "grpclb_retry_timer");
diff --git a/tools/interop_matrix/client_matrix.py b/tools/interop_matrix/client_matrix.py
index 51f04ea40b1..6bd7ff6406d 100644
--- a/tools/interop_matrix/client_matrix.py
+++ b/tools/interop_matrix/client_matrix.py
@@ -27,7 +27,7 @@ LANG_RUNTIME_MATRIX = {
     'cxx': ['cxx'],             # This is actually debian8.
     'go': ['go1.7', 'go1.8'],
     'java': ['java_oracle8'],
-    'python': ['python'],
+    #'python': ['python'],  # All python versions fail the tests due to timeout.
     'node': ['node'],
     'ruby': ['ruby'],
     'php': ['php', 'php7'],
@@ -64,14 +64,14 @@ LANG_RELEASE_MATRIX = {
         'v1.6.1',
         'v1.7.0',
     ],
-    'python': [
+    #'python': [
         #'v1.0.x',  #Fail to run the test. #13230.
-        'v1.1.4',
-        'v1.2.5',
-        'v1.3.9',
-        'v1.4.2',
-        'v1.6.6',
-    ],
+    #    'v1.1.4',
+    #    'v1.2.5',
+    #    'v1.3.9',
+    #    'v1.4.2',
+    #    'v1.6.6',
+    #],
     'node': [
         'v1.0.1',
         'v1.1.4',
@@ -97,11 +97,10 @@ LANG_RELEASE_MATRIX = {
         'v1.6.6',
     ],
    'csharp': [
-        # Fail to build images due to #13278.
         #'v1.0.1',
-        #'v1.1.4',
-        #'v1.2.5',
-        #'v1.3.9',
+        #'v1.1.4',  Fail to build.
+        #'v1.2.5',  Fail to run test with csharp image.
+        'v1.3.9',
         'v1.4.2',
         'v1.6.6',
     ],
diff --git a/tools/interop_matrix/run_interop_matrix_tests.py b/tools/interop_matrix/run_interop_matrix_tests.py
index 491438a2921..dce1033add8 100755
--- a/tools/interop_matrix/run_interop_matrix_tests.py
+++ b/tools/interop_matrix/run_interop_matrix_tests.py
@@ -83,6 +83,8 @@ argp.add_argument('--bq_result_table',
 
 args = argp.parse_args()
 
+print(str(args))
+
 
 def find_all_images_for_lang(lang):
   """Find docker images for a language across releases and runtimes.
@@ -170,7 +172,6 @@ def run_tests_for_lang(lang, runtime, images):
     jobset.message('START', 'Testing %s' % image, do_newline=True)
     # Download the docker image before running each test case.
     subprocess.check_call(['gcloud', 'docker', '--', 'pull', image])
-    _docker_images_cleanup.append(image)
     suite_name = '%s__%s_%s' % (lang, runtime, release)
     job_spec_list = find_test_cases(lang, runtime, release, suite_name)
     
@@ -197,17 +198,17 @@ def run_tests_for_lang(lang, runtime, images):
         'grpc_interop_matrix',
         suite_name,
         str(uuid.uuid4()))
+
+    if not args.keep:
+      cleanup(image)
   
   return total_num_failures
 
 
-_docker_images_cleanup = []
-def cleanup():
-  if not args.keep:
-    for image in _docker_images_cleanup:
-      dockerjob.remove_image(image, skip_nonexistent=True)
+def cleanup(image):
+  jobset.message('START', 'Cleanup docker image %s' % image, do_newline=True)
+  dockerjob.remove_image(image, skip_nonexistent=True)
 
-atexit.register(cleanup)
 
 languages = args.language if args.language != ['all'] else _LANGUAGES
 total_num_failures = 0
diff --git a/tools/jenkins/run_full_performance.sh b/tools/jenkins/run_full_performance.sh
index 195cc68003d..8657cc9a736 100755
--- a/tools/jenkins/run_full_performance.sh
+++ b/tools/jenkins/run_full_performance.sh
@@ -21,7 +21,7 @@ cd $(dirname $0)/../..
 
 # run 8core client vs 8core server
 tools/run_tests/run_performance_tests.py \
-    -l c++ csharp node ruby java python go node_express php7 php7_protobuf_c \
+    -l c++ csharp ruby java python go php7 php7_protobuf_c \
     --netperf \
     --category scalable \
     --bq_result_table performance_test.performance_experiment \