diff --git a/server/src/plugins/game-library/index.ts b/server/src/plugins/game-library/index.ts
index 143ae97..f48d0bd 100644
--- a/server/src/plugins/game-library/index.ts
+++ b/server/src/plugins/game-library/index.ts
@@ -387,19 +387,29 @@ const gameLibraryPlugin: Plugin = {
 
     // ── GET /api/game-library/common-games?users=id1,id2,... ──
     app.get('/api/game-library/common-games', (req, res) => {
-      const userIds = String(req.query.users || '').split(',').filter(Boolean);
-      if (userIds.length < 2) {
-        res.status(400).json({ error: 'Mindestens zwei Steam-IDs erforderlich (users=id1,id2).' });
+      const ids = String(req.query.users || '').split(',').filter(Boolean);
+      if (ids.length < 2) {
+        res.status(400).json({ error: 'Mindestens zwei Profile erforderlich (users=id1,id2).' });
         return;
       }
 
       const data = loadData(ctx);
 
-      // Validate all users exist
-      for (const id of userIds) {
-        if (!data.users[id]) {
-          res.status(404).json({ error: `Benutzer ${id} nicht gefunden.` });
-          return;
+      // Resolve profileIds → steamIds (profiles may be UUIDs from the multi-platform system)
+      const userIds: string[] = [];
+      for (const id of ids) {
+        if (data.users[id]) {
+          // Direct steamId (backwards compat)
+          userIds.push(id);
+        } else {
+          const profile = data.profiles[id];
+          if (profile?.steamId && data.users[profile.steamId]) {
+            userIds.push(profile.steamId);
+          } else {
+            console.warn(`[GameLibrary] common-games: could not resolve id=${id}, profile=${!!profile}, steamId=${profile?.steamId}`);
+            res.status(404).json({ error: `Benutzer ${id} nicht gefunden oder kein Steam-Konto verknuepft.` });
+            return;
+          }
         }
       }
 
diff --git a/web/src/plugins/game-library/GameLibraryTab.tsx b/web/src/plugins/game-library/GameLibraryTab.tsx
index 02d4c99..2f30c4d 100644
--- a/web/src/plugins/game-library/GameLibraryTab.tsx
+++ b/web/src/plugins/game-library/GameLibraryTab.tsx
@@ -390,9 +390,12 @@ export default function GameLibraryTab({ data }: { data: any }) {
       if (resp.ok) {
         const d = await resp.json();
         setCommonGames(d.games || d);
+      } else {
+        console.error('[GameLibrary] common-games error:', resp.status, await resp.text().catch(() => ''));
+        setCommonGames([]);
       }
-    } catch {
-      /* silent */
+    } catch (err) {
+      console.error('[GameLibrary] common-games fetch failed:', err);
     } finally {
       setLoading(false);
     }