diff --git a/detect_secrets/settings.py b/detect_secrets/settings.py
index 0d89e6f34..eb8181b67 100644
--- a/detect_secrets/settings.py
+++ b/detect_secrets/settings.py
@@ -1,4 +1,5 @@
 import contextlib
+import threading
 from contextlib import contextmanager
 from copy import deepcopy
 from functools import lru_cache
@@ -13,6 +14,15 @@
 from .util.importlib import import_file_as_module
 
 
+# Lock to protect transient_settings from concurrent access.
+# On macOS, checkov's ParallelRunner uses ThreadPoolExecutor,
+# so all scanners share the same process and global state. Without this lock,
+# concurrent calls to transient_settings() can corrupt the LRU-cached singletons
+# (get_settings, get_plugins, get_mapping_from_secret_type_to_class), causing
+# the secrets scanner to silently produce 0 findings.
+_settings_lock = threading.Lock()
+
+
 @lru_cache(maxsize=1)
 def get_settings() -> 'Settings':
     """
@@ -77,21 +87,33 @@ def default_settings() -> Generator['Settings', None, None]:
 
 @contextmanager
 def transient_settings(config: Dict[str, Any]) -> Generator['Settings', None, None]:
-    """Allows the customizability of non-global settings per invocation."""
-    original_settings = get_settings().json()
+    """Allows the customizability of non-global settings per invocation.
+
+    Protected by _settings_lock to prevent race conditions when
+    multiple threads call this concurrently (e.g., IAC + SECRETS scanners
+    running in parallel via ThreadPoolExecutor on macOS).
+    """
+    with _settings_lock:
+        original_settings = get_settings().json()
 
-    cache_bust()
-    try:
-        yield configure_settings_from_baseline(config)
-    finally:
         cache_bust()
-        configure_settings_from_baseline(original_settings)
+        try:
+            yield configure_settings_from_baseline(config)
+        finally:
+            cache_bust()
+            configure_settings_from_baseline(original_settings)
 
 
 def cache_bust() -> None:
     get_plugins.cache_clear()
 
     get_filters.cache_clear()
+
+    # BCE-56937: Clear the plugin-type mapping cache to prevent stale mappings
+    # built from empty settings during a race window.
+    from .core.plugins.util import get_mapping_from_secret_type_to_class
+    get_mapping_from_secret_type_to_class.cache_clear()
+
     for path in get_settings().filters:
         # Need to also clear the individual caches (e.g. cached regex patterns).
         parts = urlparse(path)