diff --git a/atlas/templates/atlas/collection_detail.html b/atlas/templates/atlas/collection_detail.html
index 84ff763b..bdef8850 100644
--- a/atlas/templates/atlas/collection_detail.html
+++ b/atlas/templates/atlas/collection_detail.html
@@ -19,6 +19,11 @@
                         <h2 class="card-title mb-2">{{ collection.name }}</h2>
 
                         {% include 'exam_notes.html' %}
+                        {% if casesdetails|length > 20 %}
+                            <div class="alert alert-warning" role="alert">
+                                <strong>Performance warning:</strong> This collection contains {{ casesdetails|length }} cases — in some situations this may adversely affect performance, all features will still work but page loading may be slower. Consider splitting into smaller collections if performance is an issue.
+                            </div>
+                        {% endif %}
 
                         <p class="mb-1">
                         </p>
diff --git a/templates/404.html b/templates/404.html
index 7f35606d..ed3aec80 100644
--- a/templates/404.html
+++ b/templates/404.html
@@ -3,6 +3,7 @@
 {% block content %}
     <div class="">
         <h2>404 error</h2>
+        {% if request.user.is_staff%}
         {% if reason %}
             {{ reason }}
         {% endif %}
@@ -10,5 +11,6 @@
         {% if resolved %}
             <h3>{{ resolved }}</h3>
         {% endif %}
+        {% endif %}
     </div>
 {% endblock %}
\ No newline at end of file