diff --git a/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Configuration/ui.js b/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Configuration/ui.js
index 0bb7d35..2693524 100644
--- a/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Configuration/ui.js
+++ b/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Configuration/ui.js
@@ -46,13 +46,22 @@
 
     function getItemIdFromUrl() {
         const params = new URLSearchParams(window.location.search);
-        return params.get('id');
+        return normalizeJellyfinId(params.get('id'));
+    }
+
+    function normalizeJellyfinId(value) {
+        if (!value) {
+            return null;
+        }
+
+        const normalized = value.replace(/-/g, '').toLowerCase();
+        return /^[0-9a-f]{32}$/.test(normalized) ? normalized : null;
     }
 
     async function showRecommendation() {
         const userId = ApiClient.getCurrentUserId();
         try {
-            const response = await ApiClient.getJSON(ApiClient.getUrl(`MovieNight/Users/${userId}/Recommendations`));
+            const response = await ApiClient.getJSON(ApiClient.getUrl(`MovieNight/Users/${encodeURIComponent(userId)}/Recommendations`));
             const recommendations = typeof response === 'string' ? JSON.parse(response) : response;
 
             if (recommendations && recommendations.length > 0) {
@@ -77,7 +86,7 @@
         try {
             await ApiClient.ajax({
                 type: 'POST',
-                url: ApiClient.getUrl(`MovieNight/Users/${userId}/Ratings/Films/${itemId}`),
+                url: ApiClient.getUrl(`MovieNight/Users/${encodeURIComponent(userId)}/Ratings/Films/${encodeURIComponent(itemId)}`),
                 data: JSON.stringify({ score: parseInt(score), note: 'From Jellyfin UI' }),
                 contentType: 'application/json'
             });
@@ -88,7 +97,18 @@
         }
     }
 
-    const observer = new MutationObserver(injectUI);
+    let pendingInjection = false;
+    const observer = new MutationObserver(() => {
+        if (pendingInjection) {
+            return;
+        }
+
+        pendingInjection = true;
+        requestAnimationFrame(() => {
+            pendingInjection = false;
+            injectUI();
+        });
+    });
     observer.observe(document.body, { childList: true, subtree: true });
 
     // Initial call
diff --git a/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Controllers/MovieNightController.cs b/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Controllers/MovieNightController.cs
index 49c8fbe..542ddb9 100644
--- a/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Controllers/MovieNightController.cs
+++ b/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Controllers/MovieNightController.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Security.Claims;
 using System.Threading;
 using System.Threading.Tasks;
 using Jellyfin.Plugin.MovieNight.Services;
@@ -88,7 +89,12 @@ public class MovieNightController : ControllerBase
         [FromQuery] int limit = 10,
         CancellationToken cancellationToken = default)
     {
-        return await _backendClient.GetRecommendationsAsync(userId, contentType, mood, limit, cancellationToken).ConfigureAwait(false);
+        if (!TryValidateCurrentUserId(userId, out var authenticatedUserId, out var errorResult))
+        {
+            return errorResult!;
+        }
+
+        return await _backendClient.GetRecommendationsAsync(authenticatedUserId, contentType, mood, limit, cancellationToken).ConfigureAwait(false);
     }
 
     /// <summary>
@@ -101,7 +107,12 @@ public class MovieNightController : ControllerBase
         [FromBody] RatingRequest request,
         CancellationToken cancellationToken)
     {
-        await _backendClient.PostRatingAsync(userId, filmId, request.Score, request.Note, cancellationToken).ConfigureAwait(false);
+        if (!TryValidateCurrentUserId(userId, out var authenticatedUserId, out var errorResult))
+        {
+            return errorResult!;
+        }
+
+        await _backendClient.PostRatingAsync(authenticatedUserId, filmId, request.Score, request.Note, cancellationToken).ConfigureAwait(false);
         return Ok();
     }
 
@@ -115,9 +126,42 @@ public class MovieNightController : ControllerBase
         [FromBody] ViewedRequest request,
         CancellationToken cancellationToken)
     {
-        await _backendClient.MarkViewedAsync(userId, filmId, request.WatchedAt, cancellationToken).ConfigureAwait(false);
+        if (!TryValidateCurrentUserId(userId, out var authenticatedUserId, out var errorResult))
+        {
+            return errorResult!;
+        }
+
+        await _backendClient.MarkViewedAsync(authenticatedUserId, filmId, request.WatchedAt, cancellationToken).ConfigureAwait(false);
         return Ok();
     }
+
+    private bool TryValidateCurrentUserId(string routeUserId, out string authenticatedUserId, out ActionResult? errorResult)
+    {
+        authenticatedUserId = NormalizeId(
+            HttpContext.User.FindFirstValue(ClaimTypes.NameIdentifier) ??
+            HttpContext.User.FindFirstValue("JellyfinUserId") ??
+            HttpContext.User.FindFirstValue("UserId"));
+        if (string.IsNullOrWhiteSpace(authenticatedUserId))
+        {
+            errorResult = Unauthorized();
+            return false;
+        }
+
+        var normalizedRouteUserId = NormalizeId(routeUserId);
+        if (!string.Equals(authenticatedUserId, normalizedRouteUserId, StringComparison.OrdinalIgnoreCase))
+        {
+            errorResult = Forbid();
+            return false;
+        }
+
+        errorResult = null;
+        return true;
+    }
+
+    private static string NormalizeId(string? value)
+    {
+        return Guid.TryParse(value, out var parsedGuid) ? parsedGuid.ToString("N") : string.Empty;
+    }
 }
 
 /// <summary>
diff --git a/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Services/MovieNightPeriodicSyncService.cs b/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Services/MovieNightPeriodicSyncService.cs
index bd72c5e..e193b02 100644
--- a/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Services/MovieNightPeriodicSyncService.cs
+++ b/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Services/MovieNightPeriodicSyncService.cs
@@ -1,14 +1,6 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
-using MediaBrowser.Controller.Library;
-using MediaBrowser.Controller.Entities;
-using MediaBrowser.Controller.Entities.Movies;
-using MediaBrowser.Model.Entities;
-using MediaBrowser.Model.Querying;
-using Jellyfin.Data.Enums;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 
diff --git a/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Services/MovieNightSyncService.cs b/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Services/MovieNightSyncService.cs
index f0b31f1..39d6ca9 100644
--- a/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Services/MovieNightSyncService.cs
+++ b/plugins/jellyfin/Jellyfin.Plugin.MovieNight/Services/MovieNightSyncService.cs
@@ -59,9 +59,32 @@ public class MovieNightSyncService
 
         foreach (var item in items)
         {
+            cancellationToken.ThrowIfCancellationRequested();
+
             if (item is not Movie movie) continue;
 
             var jellyfinItemId = movie.Id.ToString("N");
+            var userStates = new List<object>();
+
+            foreach (var user in users)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+
+                var userData = _userDataManager.GetUserData(user, movie);
+                if (userData is null || (!userData.Played && userData.PlayCount == 0 && userData.LastPlayedDate is null && userData.Rating is null))
+                {
+                    continue;
+                }
+
+                userStates.Add(new
+                {
+                    jellyfinUserId = user.Id.ToString("N"),
+                    isViewed = userData.Played,
+                    playCount = userData.PlayCount,
+                    lastPlayedAt = userData.LastPlayedDate,
+                    userRating = userData.Rating
+                });
+            }
 
             var itemData = new Dictionary<string, object?>
             {
@@ -74,16 +97,7 @@ public class MovieNightSyncService
                 ["genres"] = movie.Genres,
                 ["imdbId"] = movie.GetProviderId(MetadataProvider.Imdb),
                 ["tmdbId"] = movie.GetProviderId(MetadataProvider.Tmdb),
-                ["userStates"] = users.Select(u => {
-                    var userData = _userDataManager.GetUserData(u, movie);
-                    return new {
-                        jellyfinUserId = u.Id.ToString("N"),
-                        isViewed = userData?.Played ?? false,
-                        playCount = userData?.PlayCount ?? 0,
-                        lastPlayedAt = userData?.LastPlayedDate,
-                        userRating = userData?.Rating
-                    };
-                }).ToList()
+                ["userStates"] = userStates
             };
 
             syncItems.Add(itemData);