diff --git a/src/modules/csm/checkpoint.py b/src/modules/csm/checkpoint.py
index b16f35f0f..480518aac 100644
--- a/src/modules/csm/checkpoint.py
+++ b/src/modules/csm/checkpoint.py
@@ -1,14 +1,15 @@
 import logging
 import time
-from threading import Thread
+from threading import Thread, Lock
 from typing import cast
 
-from src.modules.csm.typings import FramePerformance, AttestationsAggregate
+from src.modules.csm.typings import FramePerformance
 from src.providers.consensus.client import ConsensusClient
-from src.typings import EpochNumber, BlockRoot, SlotNumber, BlockStamp, ValidatorIndex
+from src.typings import EpochNumber, BlockRoot, SlotNumber, BlockStamp
 from src.utils.web3converter import Web3Converter
 
 logger = logging.getLogger(__name__)
+lock = Lock()
 
 
 class CheckpointsFactory:
@@ -115,7 +116,7 @@ def _select_roots_to_check(
         roots_to_check = []
         slots = range(
             self.converter.get_epoch_first_slot(duty_epoch),
-            self.converter.get_epoch_last_slot(EpochNumber(duty_epoch + 1))
+            self.converter.get_epoch_last_slot(EpochNumber(duty_epoch + 1)) + 1
         )
         for slot in slots:
             # TODO: get the magic number from the CL spec
@@ -145,22 +146,19 @@ def _process_epoch(
                 continue
             slot_data = self.cc.get_block_details_raw(BlockRoot(root))
             self._process_attestations(slot_data, committees)
-
-        self.frame_performance.processed.add(EpochNumber(duty_epoch))
-        self.frame_performance.dump()
+        with lock:
+            self.frame_performance.dump(duty_epoch, committees)
         logger.info({"msg": f"Epoch {duty_epoch} processed in {time.time() - start:.2f} seconds"})
 
     def _prepare_committees(self, last_finalized_blockstamp: BlockStamp, epoch: int) -> dict:
         start = time.time()
         committees = {}
         for committee in self.cc.get_attestation_committees(last_finalized_blockstamp, EpochNumber(epoch)):
-            committees[f"{committee.slot}{committee.index}"] = committee.validators
+            validators = []
             for validator in committee.validators:
-                val = self.frame_performance.aggr_per_val.get(
-                    ValidatorIndex(int(validator)), AttestationsAggregate(0, 0)
-                )
-                val.assigned += 1
-                self.frame_performance.aggr_per_val[ValidatorIndex(int(validator))] = val
+                data = {"index": validator, "included": False}
+                validators.append(data)
+            committees[f"{committee.slot}{committee.index}"] = validators
         logger.info({"msg": f"Committees for epoch {epoch} processed in {time.time() - start:.2f} seconds"})
         return committees
 
@@ -178,12 +176,11 @@ def to_bits(aggregation_bits: str):
             att_bits = to_bits(attestation['aggregation_bits'])
             if not committee:
                 continue
-            for index, validator in enumerate(committee):
-                if validator is None:
+            for index_in_committee, validator in enumerate(committee):
+                if validator['included']:
                     # validator has already fulfilled its duties
                     continue
-                attested = att_bits[index]
+                attested = att_bits[index_in_committee]
                 if attested:
-                    self.frame_performance.aggr_per_val[ValidatorIndex(int(validator))].included += 1
-                    # duty is fulfilled, so we can remove validator from the committee
-                    committees[committee_id][index] = None
+                    validator['included'] = True
+                    committees[committee_id][index_in_committee] = validator
diff --git a/src/modules/csm/typings.py b/src/modules/csm/typings.py
index 608ae775e..9f363ab93 100644
--- a/src/modules/csm/typings.py
+++ b/src/modules/csm/typings.py
@@ -51,14 +51,21 @@ class FramePerformance:
     to_distribute: int = 0
     last_cid: str | None = None
 
-
     @property
     def avg_perf(self) -> float:
         """Returns average performance of all validators in the cache."""
         return mean((a.perf for a in self.aggr_per_val.values()))
 
-    def dump(self) -> None:
+    def dump(self, epoch: EpochNumber, committees: dict) -> None:
         """Used to persist the current state of the structure."""
+        # TODO: persist the data. no sense to keep it in memory (except of `processed` ?)
+        self.processed.add(epoch)
+        for committee in committees.values():
+            for validator in committee:
+                perf_data = self.aggr_per_val.get(validator['index'], AttestationsAggregate(0, 0))
+                perf_data.assigned += 1
+                perf_data.included += validator['included']
+                self.aggr_per_val[validator['index']] = perf_data
 
     @classmethod
     def try_read(cls, ref_slot: SlotNumber) -> Self | None: