applying fixes

src/lerobot/policies/lingbot_va/configuration_lingbot_va.py

@@ -156,8 +156,10 @@ class LingBotVAConfig(PreTrainedConfig):
         return ConstantWithWarmupSchedulerConfig(num_warmup_steps=self.scheduler_warmup_steps)
 
     @property
-    def observation_delta_indices(self) -> None:
-        return None
+    def observation_delta_indices(self) -> list[int]:
+        temporal_downsample = 4
+        stride = max(1, self.action_per_frame // temporal_downsample)
+        return list(range(0, self.frame_chunk_size * temporal_downsample * stride, stride))
 
     @property
     def action_delta_indices(self) -> list[int]:

src/lerobot/policies/lingbot_va/modeling_lingbot_va.py

@@ -1395,7 +1395,7 @@ class LingBotVAPolicy(PreTrainedPolicy):
         pred = self.transformer(input_dict, train_mode=True)
         latent_loss, action_loss = self._flow_matching_loss(input_dict, pred)
         loss = latent_loss + action_loss
-        return loss, {"latent_loss": latent_loss.detach(), "action_loss": action_loss.detach()}
+        return loss, {"latent_loss": latent_loss.item(), "action_loss": action_loss.item()}
 
     def forward(self, batch: dict[str, Tensor]) -> tuple[Tensor, dict | None]:
         """Training forward: dual-stream flow-matching loss.