This should fix the inference

mala/common/parameters.py

@@ -1543,7 +1543,9 @@ def optuna_singlenode_setup(self, wait_time=0):
         self.hyperparameters._update_device(device_temp)
 
     @classmethod
-    def load_from_file(cls, file, save_format="json", no_snapshots=False):
+    def load_from_file(
+        cls, file, save_format="json", no_snapshots=False, force_no_ddp=False
+    ):
         """
         Load a Parameters object from a file.
 
@@ -1598,7 +1600,10 @@ def load_from_file(cls, file, save_format="json", no_snapshots=False):
                     not isinstance(json_dict[key], dict)
                     or key == "openpmd_configuration"
                 ):
-                    setattr(loaded_parameters, key, json_dict[key])
+                    if key == "use_ddp" and force_no_ddp is True:
+                        setattr(loaded_parameters, key, False)
+                    else:
+                        setattr(loaded_parameters, key, json_dict[key])
             if no_snapshots is True:
                 loaded_parameters.data.snapshot_directories_list = []
         else:
@@ -1631,7 +1636,7 @@ def load_from_pickle(cls, file, no_snapshots=False):
         )
 
     @classmethod
-    def load_from_json(cls, file, no_snapshots=False):
+    def load_from_json(cls, file, no_snapshots=False, force_no_ddp=False):
         """
         Load a Parameters object from a json file.
 
@@ -1651,5 +1656,8 @@ def load_from_json(cls, file, no_snapshots=False):
 
         """
         return Parameters.load_from_file(
-            file, save_format="json", no_snapshots=no_snapshots
+            file,
+            save_format="json",
+            no_snapshots=no_snapshots,
+            force_no_ddp=force_no_ddp,
         )

mala/network/runner.py

@@ -7,6 +7,7 @@
 import torch
 import torch.distributed as dist
 
+import mala
 from mala.common.parallelizer import get_rank
 from mala.common.parameters import ParametersRunning
 from mala.network.network import Network
@@ -145,6 +146,7 @@ def load_run(
         prepare_data=False,
         load_with_mpi=None,
         load_with_gpu=None,
+        load_with_ddp=None,
     ):
         """
         Load a run.
@@ -231,7 +233,13 @@ def load_run(
                 path, run_name + ".params." + params_format
             )
 
-        loaded_params = Parameters.load_from_json(loaded_params)
+        # Neither Predictor nor Runner classes can work with DDP.
+        if cls is mala.Trainer:
+            loaded_params = Parameters.load_from_json(loaded_params)
+        else:
+            loaded_params = Parameters.load_from_json(
+                loaded_params, force_no_ddp=True
+            )
 
         # MPI has to be specified upon loading, in contrast to GPU.
         if load_with_mpi is not None:

mala/network/trainer.py

@@ -156,6 +156,7 @@ def load_run(
         params_format="json",
         load_runner=True,
         prepare_data=True,
+        load_with_ddp=None,
     ):
         """
         Load a run.
@@ -205,6 +206,9 @@ def load_run(
             params_format=params_format,
             load_runner=load_runner,
             prepare_data=prepare_data,
+            load_with_gpu=None,
+            load_with_mpi=None,
+            load_with_ddp=load_with_ddp,
         )
 
     @classmethod