diff --git a/pyproject.toml b/pyproject.toml
index d07f19ef10986..068b929f00d76 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -63,6 +63,7 @@ module = [
     "pytorch_lightning.trainer.evaluation_loop",
     "pytorch_lightning.trainer.connectors.logger_connector",
     "pytorch_lightning.utilities.argparse",
+    "pytorch_lightning.utilities.auto_restart",
     "pytorch_lightning.utilities.cli",
     "pytorch_lightning.utilities.cloud_io",
     "pytorch_lightning.utilities.debugging",
diff --git a/pytorch_lightning/utilities/auto_restart.py b/pytorch_lightning/utilities/auto_restart.py
index 464823038ae2e..4bb9e1bc4c175 100644
--- a/pytorch_lightning/utilities/auto_restart.py
+++ b/pytorch_lightning/utilities/auto_restart.py
@@ -14,7 +14,7 @@
 
 from collections.abc import Mapping
 from copy import deepcopy
-from typing import Any, Callable, Dict, Generator, Iterator, List, Optional, Union
+from typing import Any, Callable, Dict, Generator, Iterator, List, Optional, Tuple, Union
 
 from torch.utils.data import Dataset, get_worker_info, Sampler
 from torch.utils.data.dataloader import _MultiProcessingDataLoaderIter, DataLoader, IterableDataset
@@ -34,7 +34,7 @@ class FastForwardSampler(Sampler):
     samples seen in the last iterations (for the current worker).
     """
 
-    def __init__(self, sampler: Union[Sampler, Generator], attr_name: Optional[str] = None) -> None:
+    def __init__(self, sampler: Union[Sampler, Generator, Iterator], attr_name: Optional[str] = None) -> None:
         super().__init__(data_source=None)
         self._sampler = sampler
         self.restarting: bool = False
@@ -116,12 +116,13 @@ def _compute_current_iteration(self, num_batches_processed: Optional[int] = None
 
         return current_iteration
 
-    def _load_cached_state(self):
+    def _load_cached_state(self) -> None:
         if self._cached_state_dict is None or self.worker_id not in self._cached_state_dict:
             return
         self._current_iteration = self._cached_state_dict[self.worker_id]["current_iteration"]
         # delete cached state, prevent reloading every time iter() is called
         self._cached_state_dict = None
+        return
 
 
 class CaptureIterableDataset(IterableDataset):
@@ -143,8 +144,10 @@ def __init__(self, dataset: IterableDataset) -> None:
     def sampler(self) -> Sampler:
         return self.dataset.sampler
 
-    def state_dict(self) -> Dict[str, Any]:
-        return {k: v.state_dict() for k, v in self.samplers.items()}
+    def state_dict(self) -> Optional[Dict[str, Any]]:
+        if isinstance(self.samplers, dict):
+            return {k: v.state_dict() for k, v in self.samplers.items()}
+        return {}
 
     def load_state_dict(self, state_dict: Dict[int, Any]) -> None:
         self._state_dict = deepcopy(state_dict)
@@ -232,7 +235,7 @@ def store_samplers_state_dict(iterator: Iterator, sampler_state_dict: List) -> N
             iterator._sampler_state_dict_cache = sampler_state_dict
 
     @staticmethod
-    def _sanitize_batch_from_sampler_state(data: Any, state_dicts: List):
+    def _sanitize_batch_from_sampler_state(data: Any, state_dicts: List) -> Any:
         """
         This function is used to remove the sampler state dict from provided data batch.
         The custom data has this format:
@@ -255,7 +258,7 @@ def _sanitize_batch_from_sampler_state(data: Any, state_dicts: List):
         will extract the current iteration as part of the metadata returned by a custom batch.
         """
 
-        def _sanitize(data: Mapping):
+        def _sanitize(data: Mapping) -> List[Tuple[Any, Any]]:
             out = []
             for k, v in data.items():
                 if k == AutoRestartBatchKeys.PL_SAMPLERS:
@@ -267,11 +270,11 @@ def _sanitize(data: Mapping):
         return apply_to_collection(data, Mapping, _sanitize)
 
     @staticmethod
-    def extract_samplers_state_dict_from_batch(batch) -> List[Dict[int, Any]]:
+    def extract_samplers_state_dict_from_batch(batch: Any) -> Tuple[Any, List[Dict[int, Any]]]:
         """
         This function is used to convert a batch into a state_dict
         """
-        samplers_state_dict = []
+        samplers_state_dict: List[Dict[int, Any]] = []
 
         batch = CaptureIterableDataset._sanitize_batch_from_sampler_state(batch, samplers_state_dict)
 
@@ -287,6 +290,7 @@ def _find_fast_forward_samplers(dataloader: DataLoader) -> Optional[FastForwardS
 
     if isinstance(dataloader.batch_sampler, FastForwardSampler):
         return dataloader.batch_sampler
+    return None
 
 
 def _cycle_to_next_worker_and_reset(dataloader: DataLoader, state_dict: Dict[str, Any]) -> Iterator:
@@ -328,22 +332,25 @@ def _cycle_to_next_worker_and_reset(dataloader: DataLoader, state_dict: Dict[str
 
 def _dataloader_to_state_dict(
     dataloader: DataLoader, iterator: Iterator, num_batches_processed: int = None
-) -> List[Dict[str, Any]]:
+) -> Dict[Union[int, str], Union[Dict[str, int], Optional[int]]]:
     """
     Convert a dataloader to its associated state dict
     """
-    out = {}
+    out: Dict[Union[int, str], Union[Dict[str, int], Optional[int]]] = {}
     if iterator is not None:
-        out.update(_find_current_worker(iterator))
+        for iterator_k, iterator_v in _find_current_worker(iterator).items():
+            out[iterator_k] = iterator_v
 
     if not isinstance(dataloader.dataset, CaptureIterableDataset):
         fast_forward_sampler = _find_fast_forward_samplers(dataloader)
         if fast_forward_sampler is not None:
-            out.update(fast_forward_sampler.state_dict(num_batches_processed=num_batches_processed))
+            samplers_state_dict = fast_forward_sampler.state_dict(num_batches_processed=num_batches_processed)
+            for sampler_k, sampler_v in samplers_state_dict.items():
+                out[sampler_k] = sampler_v
     return out
 
 
-def _dataloader_load_state_dict(dataloader: DataLoader, state_dict: List[Dict[str, Any]]) -> DataLoader:
+def _dataloader_load_state_dict(dataloader: DataLoader, state_dict: Dict[str, Any]) -> DataLoader:
     """
     Reload ``DataLoader`` fast-forward sampler state dict.
     """