diff --git a/backend/consensus/base.py b/backend/consensus/base.py
index 846dd9279..240414635 100644
--- a/backend/consensus/base.py
+++ b/backend/consensus/base.py
@@ -337,8 +337,8 @@ def contract_snapshot_factory(
     """
     try:
         contract_address = to_checksum_address(contract_address)
-    except Exception:
-        pass
+    except (ValueError, TypeError):
+        return None
     # Check if the transaction is a contract deployment and the contract address matches the transaction's to address
     if (
         transaction.type == TransactionType.DEPLOY_CONTRACT
diff --git a/backend/consensus/vrf.py b/backend/consensus/vrf.py
index 55c953600..6135e0d2d 100644
--- a/backend/consensus/vrf.py
+++ b/backend/consensus/vrf.py
@@ -6,18 +6,26 @@
 def get_validators_for_transaction(
     nodes: list[dict],
     num_validators: int | None = None,
-    rng=np.random.default_rng(seed=int(datetime.now().timestamp())),
+    rng: np.random.Generator | None = None,
 ) -> list[dict]:
     """
     Returns subset of validators for a transaction.
     The selelction and order is given by a random sampling based on the stake of the validators.
     """
+    if rng is None:
+        rng = np.random.default_rng(seed=int(datetime.now().timestamp()))
+
     if num_validators is None:
         num_validators = DEFAULT_VALIDATORS_COUNT
 
     num_validators = min(num_validators, len(nodes))
 
     total_stake = sum(validator["stake"] for validator in nodes)
+    if total_stake == 0:
+        raise ValueError(
+            "Cannot select validators: all stakes are zero. "
+            "At least one validator must have a positive stake."
+        )
     probabilities = [validator["stake"] / total_stake for validator in nodes]
 
     selected_validators = rng.choice(
diff --git a/backend/consensus/worker_service.py b/backend/consensus/worker_service.py
index 6b41ea5e9..47cada199 100644
--- a/backend/consensus/worker_service.py
+++ b/backend/consensus/worker_service.py
@@ -588,7 +588,7 @@ def health_check():
             "cpu_percent": round(process.cpu_percent(), 2),
             "memory_percent": round(process.memory_percent(), 2),
         }
-    except:
+    except Exception:
         pass
 
     # Probe local GenVM manager responsiveness.
diff --git a/backend/database_handler/accounts_manager.py b/backend/database_handler/accounts_manager.py
index 6169b5171..c15dd06a2 100644
--- a/backend/database_handler/accounts_manager.py
+++ b/backend/database_handler/accounts_manager.py
@@ -45,7 +45,7 @@ def create_new_account_with_address(self, address: str) -> Account:
         try:
             address = to_checksum_address(address)
         except Exception:
-            pass
+            raise ValueError(f"Failed to checksum address: {address}")
 
         existing_account = (
             self.session.query(CurrentState).filter(CurrentState.id == address).first()
@@ -67,7 +67,7 @@ def get_account(self, account_address: str) -> CurrentState | None:
         try:
             normalized = to_checksum_address(account_address)
         except Exception:
-            normalized = account_address
+            raise ValueError(f"Failed to checksum address: {account_address}")
         account = (
             self.session.query(CurrentState)
             .filter(CurrentState.id == normalized)
diff --git a/backend/protocol_rpc/transactions_parser.py b/backend/protocol_rpc/transactions_parser.py
index 1a0f85126..517f407b9 100644
--- a/backend/protocol_rpc/transactions_parser.py
+++ b/backend/protocol_rpc/transactions_parser.py
@@ -604,13 +604,17 @@ def decode_method_send_data(self, data: str) -> DecodedMethodSendData:
     def decode_method_call_data(self, data: str) -> DecodedMethodCallData:
         raw_bytes = eth_utils.hexadecimal.decode_hex(data)
 
+        if len(raw_bytes) == 0:
+            return DecodedMethodCallData(b"")
+
         # Remove the null byte
         if raw_bytes[-1] == 0:
             raw_bytes = raw_bytes[:-1]
 
             # Try to decode the outer list first
             if raw_bytes[0] >= 0xF8:  # Long list
-                raw_bytes = raw_bytes[2:]  # Skip list prefix and length
+                num_length_bytes = raw_bytes[0] - 0xF7
+                raw_bytes = raw_bytes[1 + num_length_bytes:]  # Skip prefix + length bytes
             elif raw_bytes[0] >= 0xC0:  # Short list
                 raw_bytes = raw_bytes[1:]  # Skip list prefix
 
diff --git a/tests/unit/test_vrf.py b/tests/unit/test_vrf.py
index 95473770e..4760b3d35 100644
--- a/tests/unit/test_vrf.py
+++ b/tests/unit/test_vrf.py
@@ -1,5 +1,6 @@
 from backend.consensus.vrf import get_validators_for_transaction
 from unittest.mock import Mock
+import pytest
 
 
 def list_of_dicts_to_set(list_of_dicts: list[dict]) -> set:
@@ -66,3 +67,21 @@ def choice_mock(a, p, size, replace):
 
     rng.choice.assert_called_once()
     assert validators == [{"stake": 3}, {"stake": 2}, {"stake": 1}]
+
+
+def test_get_validators_zero_stake_raises():
+    """When all stakes are zero, selection should raise ValueError."""
+    nodes = [{"stake": 0}, {"stake": 0}]
+    with pytest.raises(ValueError, match="all stakes are zero"):
+        get_validators_for_transaction(nodes, 1)
+
+
+def test_get_validators_rng_not_shared_between_calls():
+    """Each call without an explicit rng should get a fresh generator."""
+    nodes = [{"stake": 1}, {"stake": 2}, {"stake": 3}]
+    # Call twice without passing rng — the default must be created fresh each time.
+    v1 = get_validators_for_transaction(nodes, 1)
+    v2 = get_validators_for_transaction(nodes, 1)
+    # Both should succeed (no shared mutable state corruption).
+    assert len(v1) == 1
+    assert len(v2) == 1