diff --git a/atroposlib/api/server.py b/atroposlib/api/server.py
index 4a94c6d8..985f8213 100644
--- a/atroposlib/api/server.py
+++ b/atroposlib/api/server.py
@@ -344,6 +344,14 @@ async def info():
 
 @app.get("/batch")
 async def get_batch():
+    # Check if trainer has registered first
+    if not hasattr(app.state, "started"):
+        return {
+            "status": "error",
+            "message": "Trainer not registered. Call /register first.",
+            "batch": [],
+        }
+    
     if not app.state.started:
         app.state.started = True
 
diff --git a/example_trainer/grpo.py b/example_trainer/grpo.py
index edbc5af0..bf2140ec 100644
--- a/example_trainer/grpo.py
+++ b/example_trainer/grpo.py
@@ -178,9 +178,14 @@ def register_trainer(config: TrainingConfig):
     )
 
 
-@retry(stop=stop_after_attempt(3), wait=wait_exponential(multiplier=1, min=4, max=15))
+@retry(stop=stop_after_attempt(5), wait=wait_exponential(multiplier=1, min=2, max=30))
 def get_batch():
     data = requests.get("http://localhost:8000/batch", timeout=10).json()
+    
+    # Check if there was an error (trainer not registered)
+    if data.get("status") == "error":
+        raise RuntimeError(f"Atropos API error: {data.get('message', 'Unknown error')}")
+    
     return data
 
 
diff --git a/example_trainer/vllm_patching/weight_updater.py b/example_trainer/vllm_patching/weight_updater.py
index 5d39569e..40b446a4 100644
--- a/example_trainer/vllm_patching/weight_updater.py
+++ b/example_trainer/vllm_patching/weight_updater.py
@@ -143,6 +143,11 @@ def weight_updater_process(
         )
         print("[Updater] ✓ NCCL group created", flush=True)
         
+        # Barrier synchronization to confirm both sides are ready
+        print("[Updater] Waiting for trainer to be ready...", flush=True)
+        dist.barrier(group=gloo_group)
+        print("[Updater] ✓ Trainer is ready, starting update loop", flush=True)
+        
     except Exception as e:
         print(f"[Updater] Failed to create process groups: {e}", flush=True)
         import traceback
@@ -212,6 +217,17 @@ def weight_updater_process(
                 if debug or (update_count % 50 == 0):
                     print(f"[Updater] Updated {param_name} (#{update_count})", flush=True)
                 
+            except torch.distributed.DistBackendError as e:
+                # NCCL communication failure - likely trainer crashed
+                error_str = str(e)
+                if "Broken pipe" in error_str or "Connection reset" in error_str:
+                    print("[Updater] Trainer disconnected (broken pipe). Exiting.", flush=True)
+                    break
+                else:
+                    print(f"[Updater] NCCL error: {e}", flush=True)
+                    import traceback
+                    traceback.print_exc()
+                    time.sleep(1)
             except Exception as e:
                 print(f"[Updater] Error in update loop: {e}", flush=True)
                 import traceback
diff --git a/example_trainer/vllm_weight_bridge.py b/example_trainer/vllm_weight_bridge.py
index fd3d66eb..5307bd54 100644
--- a/example_trainer/vllm_weight_bridge.py
+++ b/example_trainer/vllm_weight_bridge.py
@@ -336,6 +336,14 @@ class VLLMWeightBridge:
             group_name="weight_update_group",
         )
         print("[Bridge] ✓ NCCL group created")
+        
+        # Barrier synchronization to ensure both sides are ready
+        print("[Bridge] Waiting for all ranks to be ready...")
+        try:
+            dist.barrier(group=self.gloo_group)
+            print("[Bridge] ✓ All ranks synchronized and ready")
+        except Exception as e:
+            print(f"[Bridge] Warning: Barrier sync failed: {e}")
     
     def _initialize_http_mode(self) -> None:
         """Initialize HTTP-based weight synchronization (fallback)."""