Platform version 10.3.2.7882. Using the default customErrors configuration:
<customErrors mode="RemoteOnly" redirectMode="ResponseRewrite" defaultRedirect="~/error.aspx">
<error statusCode="404" redirect="~/utility/error-notfound"/>
</customErrors>
If the SiteSqlServer connection string is invalid or the SQL Server is unavailable, an ASP.NET Server Error message is displayed to the remote client instead of the expected generic message within ~/error.aspx. ~/error.aspx exists and is reachable whenever SQL Server is available.
ASP.NET message:
Can the platform be configured to show a custom error when SQL Server is down?