diff --git a/changes/v4.4.15-en.md b/changes/v4.4.15-en.md
index 800992cd0..88ad61ca6 100644
--- a/changes/v4.4.15-en.md
+++ b/changes/v4.4.15-en.md
@@ -8,3 +8,10 @@
 
 - Fix the problem that new MQTT TLS connections failed to establish after release hot upgrade [#9810](https://github.com/emqx/emqx/pull/9810).
   For more detailed information please see: [emqx/esockd#170](https://github.com/emqx/esockd/pull/170).
+
+- Fix a problem in the log message format of MQTT packets [#9858](https://github.com/emqx/emqx/pull/9858).
+  Before this fix, a comma was missing between the flags (DUP) of the fixed header
+  and the fields (ClientId) of the variable header:
+  ```
+  2023-01-29T13:40:36.567692+08:00 [debug] 127.0.0.1:50393 [MQTT] RECV CONNECT(Q0, R0, D0ClientId=test_client, ... Password=undefined)
+  ```
diff --git a/changes/v4.4.15-zh.md b/changes/v4.4.15-zh.md
index cb29bcfaa..6d2859e82 100644
--- a/changes/v4.4.15-zh.md
+++ b/changes/v4.4.15-zh.md
@@ -8,3 +8,9 @@
 
 - 修复版本热升级之后，新的 MQTT TLS 连接建立失败的问题 [#9810](https://github.com/emqx/emqx/pull/9810)。
   详情见：[emqx/esockd#170](https://github.com/emqx/esockd/pull/170)
+
+- 修复 MQTT 报文的日志打印格式的问题 [#9858](https://github.com/emqx/emqx/pull/9858)。
+  在此修复之前，固定报文头的标志位（DUP）和后面的可变报文头的字段（ClientId）之间漏掉了一个逗号做分隔：
+  ```
+  2023-01-29T13:40:36.567692+08:00 [debug] 127.0.0.1:50393 [MQTT] RECV CONNECT(Q0, R0, D0ClientId=test_client, ... Password=undefined)
+  ```
diff --git a/src/emqx.appup.src b/src/emqx.appup.src
index ebb567dbd..d25adf12f 100644
--- a/src/emqx.appup.src
+++ b/src/emqx.appup.src
@@ -3,21 +3,27 @@
 {VSN,
   [{"4.4.14",
     [{load_module,emqx_misc,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
+     {load_module,emqx_relup,brutal_purge,soft_purge,[]},
+     {load_module,emqx_app,brutal_purge,soft_purge,[]},
      {load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]}]},
    {"4.4.13",
     [{load_module,emqx_misc,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
      {load_module,emqx_cm,brutal_purge,soft_purge,[]},
      {load_module,emqx_relup,brutal_purge,soft_purge,[]},
      {load_module,emqx_app,brutal_purge,soft_purge,[]}]},
    {"4.4.12",
     [{load_module,emqx_misc,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
      {load_module,emqx_cm,brutal_purge,soft_purge,[]},
      {load_module,emqx_relup,brutal_purge,soft_purge,[]},
      {load_module,emqx_app,brutal_purge,soft_purge,[]}]},
    {"4.4.11",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {add_module,emqx_cover},
      {load_module,emqx_relup,brutal_purge,soft_purge,[]},
      {load_module,emqx_misc,brutal_purge,soft_purge,[]},
@@ -27,6 +33,7 @@
      {load_module,emqx_channel,brutal_purge,soft_purge,[]}]},
    {"4.4.10",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {add_module,emqx_cover},
      {add_module,emqx_ocsp_cache},
      {add_module,emqx_crl_cache},
@@ -48,6 +55,7 @@
                          [gen_rpc,insecure_auth_fallback_allowed,true]}}]},
    {"4.4.9",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {add_module,emqx_cover},
      {add_module,emqx_ocsp_cache},
      {add_module,emqx_crl_cache},
@@ -75,6 +83,7 @@
                          [gen_rpc,insecure_auth_fallback_allowed,true]}}]},
    {"4.4.8",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {add_module,emqx_cover},
      {add_module,emqx_ocsp_cache},
      {add_module,emqx_crl_cache},
@@ -103,6 +112,7 @@
                          [gen_rpc,insecure_auth_fallback_allowed,true]}}]},
    {"4.4.7",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {add_module,emqx_cover},
      {add_module,emqx_ocsp_cache},
      {add_module,emqx_crl_cache},
@@ -131,6 +141,7 @@
                          [gen_rpc,insecure_auth_fallback_allowed,true]}}]},
    {"4.4.6",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {add_module,emqx_cover},
      {add_module,emqx_ocsp_cache},
      {add_module,emqx_crl_cache},
@@ -159,6 +170,7 @@
                          [gen_rpc,insecure_auth_fallback_allowed,true]}}]},
    {"4.4.5",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {add_module,emqx_cover},
      {add_module,emqx_ocsp_cache},
      {add_module,emqx_crl_cache},
@@ -189,6 +201,7 @@
                          [gen_rpc,insecure_auth_fallback_allowed,true]}}]},
    {"4.4.4",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {add_module,emqx_cover},
      {add_module,emqx_ocsp_cache},
      {add_module,emqx_crl_cache},
@@ -418,21 +431,27 @@
    {<<".*">>,[]}],
   [{"4.4.14",
     [{load_module,emqx_misc,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
+     {load_module,emqx_relup,brutal_purge,soft_purge,[]},
+     {load_module,emqx_app,brutal_purge,soft_purge,[]},
      {load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]}]},
    {"4.4.13",
     [{load_module,emqx_misc,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
      {load_module,emqx_cm,brutal_purge,soft_purge,[]},
      {load_module,emqx_relup,brutal_purge,soft_purge,[]},
      {load_module,emqx_app,brutal_purge,soft_purge,[]}]},
    {"4.4.12",
     [{load_module,emqx_misc,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
      {load_module,emqx_cm,brutal_purge,soft_purge,[]},
      {load_module,emqx_relup,brutal_purge,soft_purge,[]},
      {load_module,emqx_app,brutal_purge,soft_purge,[]}]},
    {"4.4.11",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_relup,brutal_purge,soft_purge,[]},
      {load_module,emqx_app,brutal_purge,soft_purge,[]},
      {load_module,emqx_misc,brutal_purge,soft_purge,[]},
@@ -442,6 +461,7 @@
      {delete_module,emqx_cover}]},
    {"4.4.10",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_listeners,brutal_purge,soft_purge,[]},
      {load_module,emqx_kernel_sup,brutal_purge,soft_purge,[]},
      {load_module,emqx_access_rule,brutal_purge,soft_purge,[]},
@@ -460,6 +480,7 @@
      {delete_module,emqx_ocsp_cache}]},
    {"4.4.9",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_listeners,brutal_purge,soft_purge,[]},
      {load_module,emqx_kernel_sup,brutal_purge,soft_purge,[]},
      {load_module,emqx_access_rule,brutal_purge,soft_purge,[]},
@@ -483,6 +504,7 @@
      {delete_module,emqx_ocsp_cache}]},
    {"4.4.8",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_listeners,brutal_purge,soft_purge,[]},
      {load_module,emqx_kernel_sup,brutal_purge,soft_purge,[]},
      {load_module,emqx_access_rule,brutal_purge,soft_purge,[]},
@@ -507,6 +529,7 @@
      {delete_module,emqx_ocsp_cache}]},
    {"4.4.7",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_listeners,brutal_purge,soft_purge,[]},
      {load_module,emqx_kernel_sup,brutal_purge,soft_purge,[]},
      {load_module,emqx_access_rule,brutal_purge,soft_purge,[]},
@@ -531,6 +554,7 @@
      {delete_module,emqx_ocsp_cache}]},
    {"4.4.6",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_listeners,brutal_purge,soft_purge,[]},
      {load_module,emqx_kernel_sup,brutal_purge,soft_purge,[]},
      {load_module,emqx_access_rule,brutal_purge,soft_purge,[]},
@@ -555,6 +579,7 @@
      {delete_module,emqx_ocsp_cache}]},
    {"4.4.5",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_listeners,brutal_purge,soft_purge,[]},
      {load_module,emqx_kernel_sup,brutal_purge,soft_purge,[]},
      {load_module,emqx_access_rule,brutal_purge,soft_purge,[]},
@@ -581,6 +606,7 @@
      {delete_module,emqx_ocsp_cache}]},
    {"4.4.4",
     [{load_module,emqx_rule_actions_trans,brutal_purge,soft_purge,[]},
+     {load_module,emqx_packet,brutal_purge,soft_purge,[]},
      {load_module,emqx_listeners,brutal_purge,soft_purge,[]},
      {load_module,emqx_kernel_sup,brutal_purge,soft_purge,[]},
      {load_module,emqx_hooks,brutal_purge,soft_purge,[]},
diff --git a/src/emqx_packet.erl b/src/emqx_packet.erl
index 080126e5d..d91ac6f44 100644
--- a/src/emqx_packet.erl
+++ b/src/emqx_packet.erl
@@ -430,7 +430,7 @@ format_header(#mqtt_packet_header{type = Type,
     Header = io_lib:format("~s(Q~p, R~p, D~p", [type_name(Type), QoS, i(Retain), i(Dup)]),
     case S == undefined of
         true -> [Header, ")"];
-        false -> [Header, S, ")"]
+        false -> [Header, ", ", S, ")"]
     end.
 
 format_variable(undefined, _) ->