diff --git a/tools/btconsole.py b/tools/btconsole.py
index 711c81a..17ae82f 100644
--- a/tools/btconsole.py
+++ b/tools/btconsole.py
@@ -923,7 +923,8 @@ class Relay:
             for other_id in sorted(self.by_host):
                 if other_id != host_id:
                     self._send_control(conn, ROUTE_PEER_UP, other_id)
-            for other in self.by_host.values():
+            for other in list(self.by_host.values()):   # snapshot: a failed
+                # send drops that peer INSIDE the loop (mutates by_host)
                 if other is not conn:
                     self._send_control(other, ROUTE_PEER_UP, host_id)
             return
@@ -990,7 +991,8 @@ class Relay:
         if conn.host_id is not None and self.by_host.get(conn.host_id) is conn:
             del self.by_host[conn.host_id]
             self.udp_endpoint.pop(conn.host_id, None)
-            for other in self.by_host.values():
+            for other in list(self.by_host.values()):   # snapshot: a failed
+                # send drops that peer INSIDE the loop (mutates by_host)
                 self._send_control(other, ROUTE_PEER_DOWN, conn.host_id)
         self._maybe_reset_round()