The slots dictionary can change during the loop.
@@ -834,7 +834,7 @@ class FormValidationAction(Action, ABC):
"""
slots: Dict[Text, Any] = tracker.slots_to_validate()
- for slot_name, slot_value in slots.items():
+ for slot_name, slot_value in list(slots.items()):
method_name = f"validate_{slot_name.replace('-','_')}"
validate_method = getattr(self, method_name, None)
