Update to 2021-12-25 20:02

roles/bookstack/templates/env.j2

@@ -23,6 +23,7 @@ CACHE_PREFIX=bookstack_{{ bookstack_id }}
 {% if bookstack_trusted_proxies | length > 0 %}
 APP_PROXIES={{ bookstack_trusted_proxies | join(',') }}
 {% endif %}
+QUEUE_CONNECTION=database
 {% for key in bookstack_settings.keys() | list %}
 {{ key }}="{{ bookstack_settings[key] }}"
 {% endfor %}