fix accel

src/lerobot/scripts/train.py

@@ -21,6 +21,7 @@ from typing import Any
 
 import torch
 from accelerate import Accelerator
+from accelerate.utils import DistributedDataParallelKwargs
 from termcolor import colored
 from torch.amp import GradScaler
 from torch.optim import Optimizer
@@ -176,9 +177,12 @@ def train(cfg: TrainPipelineConfig):
     # Initialize Accelerate if requested
     accelerator = None
     if cfg.use_accelerate:
+        # Configure DDP to handle unused parameters
+        ddp_kwargs = DistributedDataParallelKwargs(find_unused_parameters=True)
         accelerator = Accelerator(
             gradient_accumulation_steps=cfg.gradient_accumulation_steps,
             mixed_precision=cfg.mixed_precision,
+            kwargs_handlers=[ddp_kwargs],
         )
         device = accelerator.device
         if accelerator.is_main_process: