diff --git a/CHANGELOG.md b/CHANGELOG.md
index 41ce2a71185..bc2eed5a487 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+- Fixed a bug where asset, category, and entry sources defined by the `EVENT_REGISTER_SOURCES` event didn’t have any custom fields available to them, unless the `EVENT_REGISTER_FIELD_LAYOUTS` event was also used to define the available field layouts for the event-defined source. ([#16256](https://github.com/craftcms/cms/discussions/16256))
+
+## 5.5.4 - 2024-12-02
+
 - Reduced the likelihood of a deadlock error occurring when updating search indexes. ([#15221](https://github.com/craftcms/cms/issues/15221))
 - The PHP Info utility is no longer shown in environments where the `phpinfo()` function is disabled. ([#16229](https://github.com/craftcms/cms/pull/16229))
 - “View” buttons within element indexes are now disabled when the selected view mode has no applicable settings. ([#16242](https://github.com/craftcms/cms/pull/16242))
diff --git a/src/config/app.php b/src/config/app.php
index 54ac3d44dc0..3d3fa2118f6 100644
--- a/src/config/app.php
+++ b/src/config/app.php
@@ -3,7 +3,7 @@
 return [
     'id' => 'CraftCMS',
     'name' => 'Craft CMS',
-    'version' => '5.5.3',
+    'version' => '5.5.4',
     'schemaVersion' => '5.6.0.1',
     'minVersionRequired' => '4.5.0',
     'basePath' => dirname(__DIR__), // Defines the @app alias
diff --git a/src/elements/Asset.php b/src/elements/Asset.php
index 90ff6024c7f..f45b35702bf 100644
--- a/src/elements/Asset.php
+++ b/src/elements/Asset.php
@@ -447,14 +447,10 @@ public static function sourcePath(string $sourceKey, string $stepKey, ?string $c
      */
     protected static function defineFieldLayouts(?string $source): array
     {
-        if ($source !== null) {
-            $volumes = [];
-            if (preg_match('/^volume:(.+)$/', $source, $matches)) {
-                $volume = Craft::$app->getVolumes()->getVolumeByUid($matches[1]);
-                if ($volume) {
-                    $volumes[] = $volume;
-                }
-            }
+        if ($source !== null && preg_match('/^volume:(.+)$/', $source, $matches)) {
+            $volumes = array_filter([
+                Craft::$app->getVolumes()->getVolumeByUid($matches[1]),
+            ]);
         } else {
             $volumes = Craft::$app->getVolumes()->getAllVolumes();
         }
diff --git a/src/elements/Category.php b/src/elements/Category.php
index cff3c51739c..a1276195f2f 100644
--- a/src/elements/Category.php
+++ b/src/elements/Category.php
@@ -200,14 +200,10 @@ protected static function defineSources(string $context): array
      */
     protected static function defineFieldLayouts(?string $source): array
     {
-        if ($source !== null) {
-            $groups = [];
-            if (preg_match('/^group:(.+)$/', $source, $matches)) {
-                $group = Craft::$app->getCategories()->getGroupByUid($matches[1]);
-                if ($group) {
-                    $groups[] = $group;
-                }
-            }
+        if ($source !== null && preg_match('/^group:(.+)$/', $source, $matches)) {
+            $groups = array_filter([
+                Craft::$app->getCategories()->getGroupByUid($matches[1]),
+            ]);
         } else {
             $groups = Craft::$app->getCategories()->getAllGroups();
         }
diff --git a/src/elements/Entry.php b/src/elements/Entry.php
index b04cbad5fa2..63936735824 100644
--- a/src/elements/Entry.php
+++ b/src/elements/Entry.php
@@ -371,21 +371,17 @@ public static function modifyCustomSource(array $config): array
      */
     protected static function defineFieldLayouts(?string $source): array
     {
-        if ($source !== null) {
-            if ($source === '*') {
-                $sections = Craft::$app->getEntries()->getAllSections();
-            } elseif ($source === 'singles') {
-                $sections = Craft::$app->getEntries()->getSectionsByType(Section::TYPE_SINGLE);
-            } else {
-                $sections = [];
-                if (preg_match('/^section:(.+)$/', $source, $matches)) {
-                    $section = Craft::$app->getEntries()->getSectionByUid($matches[1]);
-                    if ($section) {
-                        $sections[] = $section;
-                    }
-                }
-            }
+        if ($source === '*') {
+            $sections = Craft::$app->getEntries()->getAllSections();
+        } elseif ($source === 'singles') {
+            $sections = Craft::$app->getEntries()->getSectionsByType(Section::TYPE_SINGLE);
+        } elseif ($source !== null && preg_match('/^section:(.+)$/', $source, $matches)) {
+            $sections = array_filter([
+                Craft::$app->getEntries()->getSectionByUid($matches[1]),
+            ]);
+        }
 
+        if (isset($sections)) {
             $entryTypes = array_values(array_unique(array_merge(
                 ...array_map(fn(Section $section) => $section->getEntryTypes(), $sections),
             )));
diff --git a/src/templates/_layouts/elementindex.twig b/src/templates/_layouts/elementindex.twig
index 3932e438bc0..72c23a06218 100644
--- a/src/templates/_layouts/elementindex.twig
+++ b/src/templates/_layouts/elementindex.twig
@@ -33,8 +33,6 @@
     }) %}
 {% endif %}
 
-{% set canHaveDrafts = canHaveDrafts ?? elementInstance.hasDrafts() %}
-
 {% block sidebar %}
     {% if sources is not empty %}
         {{ tag('a', {
diff --git a/src/web/View.php b/src/web/View.php
index ff34fb149ef..532b7c9ad08 100644
--- a/src/web/View.php
+++ b/src/web/View.php
@@ -2417,6 +2417,7 @@ private function _prepareElementIndexVariables(array &$context): null
 
         $context['elementDisplayName'] = $elementType::displayName();
         $context['elementPluralDisplayName'] = $elementType::pluralDisplayName();
+        $context['canHaveDrafts'] ??= $elementType::hasDrafts();
 
         return null;
     }