diff --git a/klippy/extras/motion_report.py b/klippy/extras/motion_report.py
index 34fc455d..d32de43f 100644
--- a/klippy/extras/motion_report.py
+++ b/klippy/extras/motion_report.py
@@ -17,29 +17,37 @@ class APIDumpHelper:
         if startstop_cb is None:
             startstop_cb = (lambda is_start: None)
         self.startstop_cb = startstop_cb
+        self.is_started = False
         self.update_interval = update_interval
         self.update_timer = None
         self.clients = {}
     def _stop(self):
         self.clients.clear()
-        if self.update_timer is None:
-            return
         reactor = self.printer.get_reactor()
         reactor.unregister_timer(self.update_timer)
         self.update_timer = None
+        if not self.is_started:
+            return reactor.NEVER
         try:
             self.startstop_cb(False)
         except self.printer.command_error as e:
             logging.exception("API Dump Helper stop callback error")
+            self.clients.clear()
+        self.is_started = False
+        if self.clients:
+            # New client started while in process of stopping
+            self._start()
         return reactor.NEVER
     def _start(self):
-        if self.update_timer is not None:
+        if self.is_started:
             return
+        self.is_started = True
         try:
             self.startstop_cb(True)
         except self.printer.command_error as e:
             logging.exception("API Dump Helper start callback error")
-            self._stop()
+            self.is_started = False
+            self.clients.clear()
             raise
         reactor = self.printer.get_reactor()
         systime = reactor.monotonic()