diff --git a/apps/emqx/rebar.config b/apps/emqx/rebar.config
index 263de55f1..d84ddfd39 100644
--- a/apps/emqx/rebar.config
+++ b/apps/emqx/rebar.config
@@ -29,7 +29,7 @@
     {esockd, {git, "https://github.com/emqx/esockd", {tag, "5.9.2"}}},
     {ekka, {git, "https://github.com/emqx/ekka", {tag, "0.12.8"}}},
     {gen_rpc, {git, "https://github.com/emqx/gen_rpc", {tag, "2.8.1"}}},
-    {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.28.0"}}},
+    {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.28.1"}}},
     {pbkdf2, {git, "https://github.com/emqx/erlang-pbkdf2.git", {tag, "2.0.4"}}},
     {recon, {git, "https://github.com/ferd/recon", {tag, "2.5.1"}}},
     {snabbkaffe, {git, "https://github.com/kafka4beam/snabbkaffe.git", {tag, "1.0.0"}}}
diff --git a/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl b/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
index 0430efdf2..8eab9f992 100644
--- a/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
+++ b/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
@@ -827,19 +827,24 @@ schema_converter(Options) ->
     maps:get(schema_converter, Options, fun hocon_schema_to_spec/2).
 
 serialize_hocon_error_msg({_Schema, Errors}) ->
-    Msg = lists:map(fun hocon_error/1, Errors),
-    iolist_to_binary(Msg);
+    Msg =
+        case lists:map(fun hocon_error/1, Errors) of
+            [Error0] -> Error0;
+            Errors -> Errors
+        end,
+    iolist_to_binary(io_lib:format("~0p", [Msg]));
 serialize_hocon_error_msg(Error) ->
-    iolist_to_binary(io_lib:format("~p", [Error])).
+    iolist_to_binary(io_lib:format("~0p", [Error])).
 
 hocon_error({Type, #{path := Path} = Error}) ->
     Error1 = maps:without([path, stacktrace], Error),
-    emqx_logger_jsonfmt:best_effort_json(
-        Error1#{
-            <<"path">> => sub_path(Path),
-            <<"type">> => Type
-        },
-        []
-    ).
+    Error1#{
+        path => sub_path(Path),
+        type => Type,
+        reason => remove_useless_field(maps:get(reason, Error, #{}))
+    }.
 
 sub_path(Path) -> string:trim(Path, leading, "root.").
+
+remove_useless_field(#{} = Field) -> maps:without([stacktrace], Field);
+remove_useless_field(Field) -> Field.
diff --git a/apps/emqx_prometheus/rebar.config b/apps/emqx_prometheus/rebar.config
index b26dfa05a..4c55c7d64 100644
--- a/apps/emqx_prometheus/rebar.config
+++ b/apps/emqx_prometheus/rebar.config
@@ -4,7 +4,7 @@
     {emqx, {path, "../emqx"}},
     %% FIXME: tag this as v3.1.3
     {prometheus, {git, "https://github.com/deadtrickster/prometheus.erl", {tag, "v4.8.1"}}},
-    {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.28.0"}}}
+    {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.28.1"}}}
 ]}.
 
 {edoc_opts, [{preprocess, true}]}.
diff --git a/apps/emqx_retainer/src/emqx_retainer_schema.erl b/apps/emqx_retainer/src/emqx_retainer_schema.erl
index 547b72fc5..74f1c6287 100644
--- a/apps/emqx_retainer/src/emqx_retainer_schema.erl
+++ b/apps/emqx_retainer/src/emqx_retainer_schema.erl
@@ -12,6 +12,8 @@
     [3]
 ]).
 
+-define(INVALID_SPEC(_REASON_), throw({_REASON_, #{default => ?DEFAULT_INDICES}})).
+
 namespace() -> "retainer".
 
 roots() -> ["retainer"].
@@ -124,22 +126,30 @@ retainer_indices(example) ->
 retainer_indices(default) ->
     ?DEFAULT_INDICES;
 retainer_indices(validator) ->
-    fun is_valid_index_specs/1;
+    fun check_index_specs/1;
 retainer_indices(_) ->
     undefined.
 
-is_valid_index_specs(IndexSpecs) ->
-    case lists:all(fun is_valid_index_spec/1, IndexSpecs) of
-        true ->
-            case length(IndexSpecs) =:= ordsets:size(ordsets:from_list(IndexSpecs)) of
-                true -> ok;
-                false -> {error, duplicate_index_specs}
-            end;
-        false ->
-            {error, invalid_index_spec}
-    end.
+check_index_specs([]) ->
+    ok;
+check_index_specs(IndexSpecs) when is_list(IndexSpecs) ->
+    lists:foreach(fun check_index_spec/1, IndexSpecs),
+    check_duplicate(IndexSpecs);
+check_index_specs(_IndexSpecs) ->
+    ?INVALID_SPEC(list_index_spec_limited).
 
-is_valid_index_spec(IndexSpec) ->
-    length(IndexSpec) > 0 andalso
-        lists:all(fun(Idx) -> Idx > 0 end, IndexSpec) andalso
-        IndexSpec =:= ordsets:to_list(ordsets:from_list(IndexSpec)).
+check_index_spec([]) ->
+    ?INVALID_SPEC(non_empty_index_spec_limited);
+check_index_spec(IndexSpec) when is_list(IndexSpec) ->
+    case lists:all(fun(Idx) -> is_integer(Idx) andalso Idx > 0 end, IndexSpec) of
+        false -> ?INVALID_SPEC(pos_integer_index_limited);
+        true -> check_duplicate(IndexSpec)
+    end;
+check_index_spec(_IndexSpec) ->
+    ?INVALID_SPEC(list_index_spec_limited).
+
+check_duplicate(List) ->
+    case length(List) =:= length(lists:usort(List)) of
+        false -> ?INVALID_SPEC(unique_index_spec_limited);
+        true -> ok
+    end.
diff --git a/mix.exs b/mix.exs
index 7d47a038d..d26d7f68d 100644
--- a/mix.exs
+++ b/mix.exs
@@ -66,7 +66,7 @@ defmodule EMQXUmbrella.MixProject do
       # in conflict by emqtt and hocon
       {:getopt, "1.0.2", override: true},
       {:snabbkaffe, github: "kafka4beam/snabbkaffe", tag: "1.0.0", override: true},
-      {:hocon, github: "emqx/hocon", tag: "0.28.0", override: true},
+      {:hocon, github: "emqx/hocon", tag: "0.28.1", override: true},
       {:emqx_http_lib, github: "emqx/emqx_http_lib", tag: "0.5.1", override: true},
       {:esasl, github: "emqx/esasl", tag: "0.2.0"},
       {:jose, github: "potatosalad/erlang-jose", tag: "1.11.2"},
diff --git a/rebar.config b/rebar.config
index 499e58bb5..a92eb7074 100644
--- a/rebar.config
+++ b/rebar.config
@@ -67,7 +67,7 @@
     , {system_monitor, {git, "https://github.com/ieQu1/system_monitor", {tag, "3.0.3"}}}
     , {getopt, "1.0.2"}
     , {snabbkaffe, {git, "https://github.com/kafka4beam/snabbkaffe.git", {tag, "1.0.0"}}}
-    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.28.0"}}}
+    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.28.1"}}}
     , {emqx_http_lib, {git, "https://github.com/emqx/emqx_http_lib.git", {tag, "0.5.1"}}}
     , {esasl, {git, "https://github.com/emqx/esasl", {tag, "0.2.0"}}}
     , {jose, {git, "https://github.com/potatosalad/erlang-jose", {tag, "1.11.2"}}}