diff --git a/apps/emqx/src/emqx_config.erl b/apps/emqx/src/emqx_config.erl
index d12b52639..fa2118f99 100644
--- a/apps/emqx/src/emqx_config.erl
+++ b/apps/emqx/src/emqx_config.erl
@@ -711,7 +711,7 @@ do_put(Type, Putter, [RootName | KeyPath], DeepValue) ->
     NewValue = do_deep_put(Type, Putter, KeyPath, OldValue, DeepValue),
     Key = ?PERSIS_KEY(Type, RootName),
     persistent_term:put(Key, NewValue),
-    post_save_config_hook(Key, NewValue),
+    put_config_post_change_actions(Key, NewValue),
     ok.
 
 do_deep_get(?CONF, AtomKeyPath, Map, Default) ->
@@ -918,8 +918,8 @@ rawconf_to_conf(SchemaModule, RawPath, RawValue) ->
 %% When the global zone change, the zones is updated with the new global zone.
 %% The global zone's keys is too many,
 %% so we don't choose to write a global zone change emqx_config_handler callback to hook
-post_save_config_hook(?PERSIS_KEY(?CONF, zones), _Zones) ->
+put_config_post_change_actions(?PERSIS_KEY(?CONF, zones), _Zones) ->
     emqx_flapping:update_config(),
     ok;
-post_save_config_hook(_Key, _NewValue) ->
+put_config_post_change_actions(_Key, _NewValue) ->
     ok.
diff --git a/apps/emqx/src/emqx_flapping.erl b/apps/emqx/src/emqx_flapping.erl
index 129fee012..252e47106 100644
--- a/apps/emqx/src/emqx_flapping.erl
+++ b/apps/emqx/src/emqx_flapping.erl
@@ -97,9 +97,17 @@ detect(ClientId, PeerHost, #{enable := true, max_count := Threshold} = Policy) -
 detect(_ClientId, _PeerHost, #{enable := false}) ->
     false.
 
-%% with default, if we delete Zone at running time. we should not crash.
 get_policy(Zone) ->
-    emqx_config:get_zone_conf(Zone, [flapping_detect], ?DEFAULT_POLICY).
+    Flapping = [flapping_detect],
+    case emqx_config:get_zone_conf(Zone, Flapping, undefined) of
+        undefined ->
+            %% If zone has be deleted at running time,
+            %% we don't crash the connection and disable flapping detect.
+            Policy = emqx_config:get(Flapping),
+            Policy#{enable => false};
+        Policy ->
+            Policy
+    end.
 
 now_diff(TS) -> erlang:system_time(millisecond) - TS.
 
diff --git a/apps/emqx/src/emqx_schema.erl b/apps/emqx/src/emqx_schema.erl
index 4929c2023..49d96e26a 100644
--- a/apps/emqx/src/emqx_schema.erl
+++ b/apps/emqx/src/emqx_schema.erl
@@ -33,6 +33,7 @@
 -define(MAX_INT_TIMEOUT_MS, 4294967295).
 %% floor(?MAX_INT_TIMEOUT_MS / 1000).
 -define(MAX_INT_TIMEOUT_S, 4294967).
+-define(DEFAULT_WINDOW_TIME, "1m").
 
 -type duration() :: integer().
 -type duration_s() :: integer().
@@ -275,7 +276,10 @@ roots(low) ->
         {"flapping_detect",
             sc(
                 ref("flapping_detect"),
-                #{importance => ?DEFAULT_IMPORTANCE}
+                #{
+                    importance => ?DEFAULT_IMPORTANCE,
+                    converter => fun flapping_detect_converter/2
+                }
             )},
         {"persistent_session_store",
             sc(
@@ -692,7 +696,7 @@ fields("flapping_detect") ->
             sc(
                 duration(),
                 #{
-                    default => "1m",
+                    default => ?DEFAULT_WINDOW_TIME,
                     importance => ?IMPORTANCE_HIGH,
                     desc => ?DESC(flapping_detect_window_time)
                 }
@@ -3495,3 +3499,9 @@ mqtt_converter(#{<<"keepalive_backoff">> := Backoff} = Mqtt, _Opts) ->
     Mqtt#{<<"keepalive_multiplier">> => Backoff * 2};
 mqtt_converter(Mqtt, _Opts) ->
     Mqtt.
+
+%% For backward compatibility with window_time is disable
+flapping_detect_converter(Conf = #{<<"window_time">> := <<"disable">>}, _Opts) ->
+    Conf#{<<"window_time">> => ?DEFAULT_WINDOW_TIME, <<"enable">> => false};
+flapping_detect_converter(Conf, _Opts) ->
+    Conf.
diff --git a/apps/emqx/test/emqx_flapping_SUITE.erl b/apps/emqx/test/emqx_flapping_SUITE.erl
index d377eba4a..b03334dc6 100644
--- a/apps/emqx/test/emqx_flapping_SUITE.erl
+++ b/apps/emqx/test/emqx_flapping_SUITE.erl
@@ -161,5 +161,15 @@ validate_timer(Names) ->
     ?assertEqual(maps:keys(Zones), maps:keys(Timers)),
     ok.
 
+t_window_compatibility_check(_Conf) ->
+    Flapping = emqx:get_config([flapping_detect]),
+    ok = emqx_config:init_load(emqx_schema, <<"flapping_detect {window_time = disable}">>),
+    ?assertMatch(#{window_time := 60000, enable := false}, emqx:get_config([flapping_detect])),
+    %% reset
+    FlappingBin = iolist_to_binary(["flapping_detect {", hocon_pp:do(Flapping, #{}), "}"]),
+    ok = emqx_config:init_load(emqx_schema, FlappingBin),
+    ?assertEqual(Flapping, emqx:get_config([flapping_detect])),
+    ok.
+
 get_policy(Zone) ->
     emqx_config:get_zone_conf(Zone, [flapping_detect]).