diff --git a/frontend/src/app/plugins/utils.cljs b/frontend/src/app/plugins/utils.cljs
index 5765b6cc6b..863ad37e2f 100644
--- a/frontend/src/app/plugins/utils.cljs
+++ b/frontend/src/app/plugins/utils.cljs
@@ -276,13 +276,39 @@
   (let [s (set values)]
     (if (= (count s) 1) (first s) "mixed")))
 
+(defn- flatten-error-map
+  "Walk an error map produced by `csm/interpret-schema-problem` and yield
+  `[path message]` pairs, where `path` is the dot-joined field path
+  (e.g. `:group` -> \"group\", `[:sets 0 :name]` -> \"sets.0.name\").
+
+  `interpret-schema-problem` calls `(assoc-in acc field {:message …})`, so
+  when the malli error path has more than one element the resulting map is
+  nested (e.g. `{:sets {0 {:name {:message \"…\"}}}}`); when the path has
+  a single element it is flat (`{:group {:message \"…\"}}`). The plugin
+  error-message renderer needs both cases reduced to per-leaf
+  `[path message]` pairs so it can produce one `plugins.validation.message`
+  string per actual validation problem."
+  ([m] (flatten-error-map [] m))
+  ([prefix m]
+   (mapcat
+    (fn [[k v]]
+      (let [segment (cond
+                      (keyword? k) (name k)
+                      (string?  k) k
+                      :else        (str k))
+            path    (conj prefix segment)]
+        (if (and (map? v) (not (contains? v :message)))
+          (flatten-error-map path v)
+          [[(str/join "." path) (:message v)]])))
+    m)))
+
 (defn error-messages
   [explain]
   (->> (:errors explain)
        (reduce csm/interpret-schema-problem {})
-       #_(mapcat (comp seq val))     ;; FIXME: why is this for? it breaks the message
-       (map (fn [[field {:keys [message]}]]
-              (tr "plugins.validation.message" (name field) message)))
+       (flatten-error-map)
+       (map (fn [[field message]]
+              (tr "plugins.validation.message" field message)))
        (str/join ". ")))
 
 (defn handle-error
diff --git a/frontend/test/frontend_tests/plugins/utils_test.cljs b/frontend/test/frontend_tests/plugins/utils_test.cljs
new file mode 100644
index 0000000000..8fbf4e4f40
--- /dev/null
+++ b/frontend/test/frontend_tests/plugins/utils_test.cljs
@@ -0,0 +1,56 @@
+;; This Source Code Form is subject to the terms of the Mozilla Public
+;; License, v. 2.0. If a copy of the MPL was not distributed with this
+;; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+;;
+;; Copyright (c) KALEIDOS INC
+
+(ns frontend-tests.plugins.utils-test
+  (:require
+   [app.plugins.utils :as plugins.utils]
+   [cljs.test :as t :include-macros true]))
+
+;; Access the private flattener for direct testing.
+(def ^:private flatten-error-map @#'plugins.utils/flatten-error-map)
+
+(t/deftest test-flatten-error-map-flat-input
+  ;; Regression test for issue #9417.
+  ;;
+  ;; When a malli error path has a single element, `interpret-schema-problem`
+  ;; produces a flat map. The flattener must pass that through unchanged.
+  (let [result (flatten-error-map {:group {:message "must be string"}})]
+    (t/is (= [["group" "must be string"]] result))))
+
+(t/deftest test-flatten-error-map-nested-input
+  ;; Regression test for issue #9417.
+  ;;
+  ;; When a malli error path has multiple elements, `interpret-schema-problem`
+  ;; produces a nested map via `(assoc-in acc path …)`. The old plugin
+  ;; consumer destructured assuming a flat shape, so the nested case rendered
+  ;; the message text as the field name (`Field message is invalid`) instead
+  ;; of the real validation reason. The flattener must descend until it finds
+  ;; a leaf carrying a `:message`.
+  (let [explain {:sets {0 {:name {:message "must not be empty"}}}}
+        result  (set (flatten-error-map explain))]
+    (t/is (= #{["sets.0.name" "must not be empty"]} result))))
+
+(t/deftest test-flatten-error-map-multiple-fields
+  ;; Multiple validation problems on the same explain produce multiple
+  ;; entries, none of which clobber each other.
+  (let [explain {:group {:message "must be string"}
+                 :sets  {0 {:message "set not found"}}}
+        result  (set (flatten-error-map explain))]
+    (t/is (= #{["group" "must be string"]
+               ["sets.0"  "set not found"]} result))))
+
+(t/deftest test-flatten-error-map-mixed-key-types
+  ;; Numeric indices (from vector positions in the malli path) must render
+  ;; cleanly; string keys must also be accepted alongside keywords.
+  (let [explain {:items {2 {"label" {:message "invalid label"}}}}
+        [[path message]] (flatten-error-map explain)]
+    (t/is (= "items.2.label" path))
+    (t/is (= "invalid label" message))))
+
+(t/deftest test-flatten-error-map-empty
+  ;; No validation errors -> no output (callers join with ". " and would
+  ;; otherwise emit an empty string, which is fine).
+  (t/is (empty? (flatten-error-map {}))))
diff --git a/frontend/test/frontend_tests/runner.cljs b/frontend/test/frontend_tests/runner.cljs
index 21816ba1a3..8935cd286a 100644
--- a/frontend/test/frontend_tests/runner.cljs
+++ b/frontend/test/frontend_tests/runner.cljs
@@ -24,6 +24,7 @@
    [frontend-tests.plugins.context-shapes-test]
    [frontend-tests.plugins.parser-test]
    [frontend-tests.plugins.tokens-test]
+   [frontend-tests.plugins.utils-test]
    [frontend-tests.svg-fills-test]
    [frontend-tests.tokens.import-export-test]
    [frontend-tests.tokens.logic.token-actions-test]
@@ -72,6 +73,7 @@
    'frontend-tests.plugins.context-shapes-test
    'frontend-tests.plugins.parser-test
    'frontend-tests.plugins.tokens-test
+   'frontend-tests.plugins.utils-test
    'frontend-tests.svg-fills-test
    'frontend-tests.tokens.import-export-test
    'frontend-tests.tokens.logic.token-actions-test