diff --git a/enterprise/app/models/enterprise/account/plan_usage_and_limits.rb b/enterprise/app/models/enterprise/account/plan_usage_and_limits.rb
index 705097030..0937c7b82 100644
--- a/enterprise/app/models/enterprise/account/plan_usage_and_limits.rb
+++ b/enterprise/app/models/enterprise/account/plan_usage_and_limits.rb
@@ -16,20 +16,15 @@ module Enterprise::Account::PlanUsageAndLimits # rubocop:disable Metrics/ModuleL
   end
 
   def increment_response_usage
-    current_usage = custom_attributes[CAPTAIN_RESPONSES_USAGE].to_i || 0
-    custom_attributes[CAPTAIN_RESPONSES_USAGE] = current_usage + 1
-    save
+    increment_custom_attribute(CAPTAIN_RESPONSES_USAGE)
   end
 
   def reset_response_usage
-    custom_attributes[CAPTAIN_RESPONSES_USAGE] = 0
-    save
+    update_custom_attribute(CAPTAIN_RESPONSES_USAGE, 0)
   end
 
   def update_document_usage
-    # this will ensure that the document count is always accurate
-    custom_attributes[CAPTAIN_DOCUMENTS_USAGE] = captain_documents.count
-    save
+    update_custom_attribute(CAPTAIN_DOCUMENTS_USAGE, captain_documents.count)
   end
 
   def email_transcript_enabled?
@@ -130,6 +125,27 @@ module Enterprise::Account::PlanUsageAndLimits # rubocop:disable Metrics/ModuleL
     ChatwootApp.max_limit
   end
 
+  # Atomic jsonb_set to avoid clobbering concurrent writes to other custom_attributes keys.
+  # Goes through Account relation (rather than raw connection) so shard routing is respected.
+  # rubocop:disable Rails/SkipsModelValidations
+  def update_custom_attribute(key, value)
+    Account.where(id: id).update_all([
+                                       "custom_attributes = jsonb_set(COALESCE(custom_attributes, '{}'), ARRAY[:key], :value::jsonb)",
+                                       { key: key, value: value.to_json }
+                                     ])
+    custom_attributes[key] = value
+  end
+
+  def increment_custom_attribute(key)
+    Account.where(id: id).update_all([
+                                       "custom_attributes = jsonb_set(COALESCE(custom_attributes, '{}'), ARRAY[:key], " \
+                                       '(COALESCE((custom_attributes ->> :key)::int, 0) + 1)::text::jsonb)',
+                                       { key: key }
+                                     ])
+    custom_attributes[key] = custom_attributes[key].to_i + 1
+  end
+  # rubocop:enable Rails/SkipsModelValidations
+
   def validate_limit_keys
     errors.add(:limits, ': Invalid data') unless self[:limits].is_a? Hash
     self[:limits] = {} if self[:limits].blank?
diff --git a/spec/enterprise/services/enterprise/billing/handle_stripe_event_service_spec.rb b/spec/enterprise/services/enterprise/billing/handle_stripe_event_service_spec.rb
index 0f8ce1494..f9b550ef8 100644
--- a/spec/enterprise/services/enterprise/billing/handle_stripe_event_service_spec.rb
+++ b/spec/enterprise/services/enterprise/billing/handle_stripe_event_service_spec.rb
@@ -83,6 +83,37 @@ describe Enterprise::Billing::HandleStripeEventService do
     end
   end
 
+  describe 'subscription quantity update' do
+    before do
+      allow(subscription).to receive(:[]).with('plan')
+                                         .and_return({ 'id' => 'price_startups', 'product' => 'plan_id_startups', 'name' => 'Startups' })
+    end
+
+    it 'updates subscribed_quantity' do
+      allow(subscription).to receive(:[]).with('quantity').and_return(6)
+
+      stripe_event_service.new.perform(event: event)
+
+      expect(account.reload.custom_attributes['subscribed_quantity']).to eq(6)
+    end
+
+    it 'persists quantity even when increment_response_usage runs concurrently' do
+      allow(subscription).to receive(:[]).with('quantity').and_return(6)
+      account.update!(custom_attributes: account.custom_attributes.merge('captain_responses_usage' => 100))
+
+      # Simulate: webhook updates quantity, then a concurrent increment_response_usage writes usage
+      stripe_event_service.new.perform(event: event)
+      account.reload
+
+      # Simulate concurrent increment_response_usage (atomic jsonb_set, not full hash overwrite)
+      account.increment_response_usage
+
+      # Quantity must survive the concurrent usage update
+      expect(account.reload.custom_attributes['subscribed_quantity']).to eq(6)
+      expect(account.reload.custom_attributes['captain_responses_usage']).to eq(101)
+    end
+  end
+
   describe 'subscription deletion handling' do
     it 'calls CreateStripeCustomerService on subscription deletion' do
       allow(event).to receive(:type).and_return('customer.subscription.deleted')