So, I followed the instructions in this blog post, created an error_page directory under my theme directory, placed offline.html file in there with some basic html, along with a style.css (included in the html) and an image (also included in the html), committed to the repository, created a deployment package, deployed to our acceptance environment, started the server, shut down the server, browsed to the server, and.... Green Monsters. Cleared browser cache and reloaded, still Green Monsters. Is there something I'm missing here, or is this just not working as it should? Is there some other configuration I have to set to make this work? We are in Mendix Cloud v4, by the way.
There is currently a delay of about one hour before the custom error pages are visible when the app is offline. They are not updated immediately when deploying.