diff --git a/hathor/cli/events_simulator/events_simulator.py b/hathor/cli/events_simulator/events_simulator.py
index 207618de8..a265449a8 100644
--- a/hathor/cli/events_simulator/events_simulator.py
+++ b/hathor/cli/events_simulator/events_simulator.py
@@ -14,12 +14,11 @@
 
 from argparse import ArgumentParser, Namespace
 
-from hathor.cli.events_simulator.scenario import Scenario
-
 DEFAULT_PORT = 8080
 
 
 def create_parser() -> ArgumentParser:
+    from hathor.cli.events_simulator.scenario import Scenario
     from hathor.cli.util import create_parser
 
     parser = create_parser()
diff --git a/hathor/event/event_manager.py b/hathor/event/event_manager.py
index c29a76f9b..458d4878e 100644
--- a/hathor/event/event_manager.py
+++ b/hathor/event/event_manager.py
@@ -54,6 +54,7 @@ class EventManager:
     """
 
     _peer_id: str
+    _is_running: bool = False
     _load_finished: bool = False
 
     @property
@@ -83,11 +84,17 @@ def __init__(
         self._subscribe_events()
 
     def start(self, peer_id: str) -> None:
+        assert self._is_running is False, 'Cannot start, EventManager is already running'
+
         self._peer_id = peer_id
         self._event_ws_factory.start()
+        self._is_running = True
 
     def stop(self):
+        assert self._is_running is True, 'Cannot stop, EventManager is not running'
+
         self._event_ws_factory.stop()
+        self._is_running = False
 
     def _assert_closed_event_group(self):
         # XXX: we must check that the last event either does not belong to an event group or that it just closed an
@@ -110,6 +117,8 @@ def _subscribe_events(self):
             self._pubsub.subscribe(event, self._handle_event)
 
     def _handle_event(self, event_type: HathorEvents, event_args: EventArguments) -> None:
+        assert self._is_running, 'Cannot handle event, EventManager is not started.'
+
         event_type = _EVENT_CONVERTERS.get(event_type, event_type)
         event_specific_handlers = {
             HathorEvents.LOAD_FINISHED: self._handle_load_finished
diff --git a/hathor/event/websocket/factory.py b/hathor/event/websocket/factory.py
index ed5af01e7..41b19dd14 100644
--- a/hathor/event/websocket/factory.py
+++ b/hathor/event/websocket/factory.py
@@ -48,10 +48,14 @@ def __init__(self, reactor: Reactor, event_storage: EventStorage):
 
     def start(self):
         """Start the WebSocket server. Required to be able to send events."""
+        assert self._is_running is False, 'Cannot start, EventWebsocketFactory is already running'
+
         self._is_running = True
 
     def stop(self):
         """Stop the WebSocket server. No events can be sent."""
+        assert self._is_running is True, 'Cannot stop, EventWebsocketFactory is not running'
+
         self._is_running = False
 
         for connection in self._connections:
diff --git a/hathor/manager.py b/hathor/manager.py
index 89678dcd7..ef04a2a7e 100644
--- a/hathor/manager.py
+++ b/hathor/manager.py
@@ -269,6 +269,9 @@ def start(self) -> None:
                 )
                 sys.exit(-1)
 
+        if self._event_manager:
+            self._event_manager.start(not_none(self.my_peer.id))
+
         self.state = self.NodeState.INITIALIZING
         self.pubsub.publish(HathorEvents.MANAGER_ON_START)
         self.connections.start()
@@ -305,9 +308,6 @@ def start(self) -> None:
         if self.stratum_factory:
             self.stratum_factory.start()
 
-        if self._event_manager:
-            self._event_manager.start(not_none(self.my_peer.id))
-
         # Start running
         self.tx_storage.start_running_manager()