After some time, the site started working again, but we were never able to figure out what the problem was. How can we achieve our goal and what did we do wrong?
In order to create your own custom sitemap file you can simply add the URL as a data field to each data entry in your DB that is going to be used dynamically to generate different pages…so if you have products for example and are going to show each on the product page, in the product data type add a field called URL and in that field populate it with the URL for your live app that points to the specific product.
Then you can download that via CSV export. Then create your own sitemap file (lots of websites found via Google search on how to structure properly)…once you have created the sitemap, upload it via your settings tab.