diff --git a/app/services/osuny/category/optimizer.rb b/app/services/osuny/category/optimizer.rb
new file mode 100644
index 000000000..920d309e3
--- /dev/null
+++ b/app/services/osuny/category/optimizer.rb
@@ -0,0 +1,66 @@
+# Charge toutes les catégories d'une université en une seule requête et remonte
+# la chaîne de parents en mémoire, pour afficher un objet categorizable groupé
+# par taxonomie sans le N+1 de la récursion `descendants_and_self`.
+module Osuny
+  module Category
+    class Optimizer
+      def initialize(about)
+        @about = about
+      end
+
+      # { taxonomie => [catégories de about rattachées à cette taxonomie] },
+      # ordonné, limité aux taxonomies qui ont au moins une catégorie utilisée.
+      #
+      # Exemple : { #<Taxonomy "Pays"> => [#<Category "France">, #<Category "Italie">] }
+      def groups_by_taxonomy
+        @groups_by_taxonomy ||= taxonomies.each_with_object({}) do |taxonomy, hash|
+          used = about_categories_by_root[taxonomy]
+          hash[taxonomy] = used if used.present?
+        end
+      end
+
+      # Catégories de about qui sont elles-mêmes racines et non-taxonomies.
+      #
+      # Exemple : [#<Category "Actualité">, #<Category "Événement">]
+      def free_categories
+        @free_categories ||= about_categories.select { |c| c.parent_id.nil? && !c.is_taxonomy }
+      end
+
+      protected
+
+      def about_categories
+        @about_categories ||= @about.categories.includes(:localizations).to_a
+      end
+
+      def categories_by_id
+        @categories_by_id ||= categories_class.where(university: university)
+                                              .includes(:localizations)
+                                              .index_by(&:id)
+      end
+
+      def categories_class
+        @categories_class ||= @about.categories.klass
+      end
+
+      def university
+        @university ||= @about.university
+      end
+
+      def taxonomies
+        @taxonomies ||= categories_by_id.values
+                                        .select { |c| c.parent_id.nil? && c.is_taxonomy }
+                                        .sort_by(&:position)
+      end
+
+      def about_categories_by_root
+        @about_categories_by_root ||= about_categories.group_by { |c| root_of(c) }
+      end
+
+      def root_of(category)
+        current = category
+        current = categories_by_id[current.parent_id] while current && current.parent_id
+        current
+      end
+    end
+  end
+end
diff --git a/app/views/admin/application/categories/widget/_show.html.erb b/app/views/admin/application/categories/widget/_show.html.erb
index 539f00cce..18f3ec59f 100644
--- a/app/views/admin/application/categories/widget/_show.html.erb
+++ b/app/views/admin/application/categories/widget/_show.html.erb
@@ -1,20 +1,11 @@
 <%
-categories_class = about.categories.klass
-categories_in_university = categories_class.where(university: current_university)
-taxonomies = categories_in_university.taxonomies.ordered
-free_categories = categories_in_university.free
-free_categories_in_use = about.categories.merge(free_categories)
+optimizer = Osuny::Category::Optimizer.new(about)
 columns ||= 1
 classes = "col-lg-#{12/columns}"
 # TODO manage child free categories
 %>
 <div class="row">
-<% 
-# First, taxonomies
-taxonomies.each do |taxonomy|
-  taxons_in_use = about.categories.merge(taxonomy.descendants_and_self)
-  next if taxons_in_use.none?
-  %>
+<% optimizer.groups_by_taxonomy.each do |taxonomy, taxons_in_use| %>
   <div class="<%= classes %> mb-4">
     <%= osuny_label taxonomy.to_s_in(current_language) %>
     <ul class="list-unstyled">
@@ -24,13 +15,11 @@ taxonomies.each do |taxonomy|
     </ul>
   </div>
 <% end %>
-<% 
-# Then, free categories
-if free_categories_in_use.any? %>
+<% if optimizer.free_categories.any? %>
   <div class="<%= classes %> mb-4">
     <%= osuny_label t('category.title') %>
     <ul class="list-unstyled">
-      <% free_categories_in_use.each do |category| %>
+      <% optimizer.free_categories.each do |category| %>
         <li><%= osuny_link_localized_if can?(:read, category), category, [:admin, category] %></li>
       <% end %>
     </ul>
diff --git a/config/initializers/bugsnag.rb b/config/initializers/bugsnag.rb
index fcb07f2ae..ca5fca160 100644
--- a/config/initializers/bugsnag.rb
+++ b/config/initializers/bugsnag.rb
@@ -26,4 +26,15 @@
     next unless user_agent.include?('ChatGPT-User')
     false
   end)
+
+  config.add_on_error(proc do |event|
+    next unless event.metadata.key?(:active_job)
+    ignored_error_classes = [
+      "GoodJob::ActiveJobExtensions::Concurrency::ConcurrencyExceededError",
+      "Communication::Website::LockError"
+    ]
+    error_class = event.exceptions.first[:errorClass]
+    next unless ignored_error_classes.include?(error_class)
+    false
+  end)
 end