SSRS Error: Dynamic packer query not found

Once again I came across an SSRS error, telling me the dynamic packed query was not found.
\Classes\SRSQueryBuilder\initalize (21)

The environment has 3 AOS, all of them running on one windows server (2712/8101, 2713/8102, 2714/8103) and 3 SSRS instances all running on another windows server. Since default AX voodoo like restart and incremental IL did not resolve the problem, I check and corrected issues following this checklist

In Dynamics AX

• All AX instances have the BC Proxy account configured as system service account under
  System Administration > Setup > System > System service account
• Every AX instance has its own SSRS report server configured
  System Administration > Setup > Business Intelligence > Reporting Services > Report Server
• There is only one default configuration
• The name (of the windows server) is correct e.g. VM-SRV-SQL
• The name of the SSRS instance (!) is correct and configured e.g. MSSQLSERER, SSRSLIVE, SSRSTEST,etc.
• Check the URL (they are in reverse order in the SSRS configuration manager) *argh*
    The report manager url is correct. That’s where you can browse the folder and set permissions
    The report service url is corret. That’s the web service
• The configuration is assigned to the correct AOS
  Check the online users form if you are not sure which AOS you are actually using

On the SSRS server

• All SSRS instances are running and all SSRS instances run as BC Proxy account
• The default configuration (that cannot be changed in the AX configuration utility) is valid
• The SSRS instances have a valid Microsoft.Dynamics.AX.ReportConfiguration.axc.configuration file in the Report Server\bin directory. If you are not sure, create a new configuration using the configuration utility, test the configuration by starting AX, save the configuration as file and replace the old one in the Report Server\Bin directory
• Make sure the Business Connector configuration has a default company name e.g. DAT
• Restart the SSRS instances