Indeed, HTML5 report viewer uses Reporting REST service in order to display reports. Therefore, run-time changes to report needs to be inside the custom report resolver
that is used by the service. Resolver's Resolve() method will be called several times, it will happen each time when the Reporting engine needs the report source.
To avoid retrieving of the data each time the Resolve() method is called, my recommendation is to consider using a custom cache where the already created data object can be saved and retrieved from. Report can connect to the data object using ObjectDataSource
which DataMember property is set to the method that retrieves the data object from the cache or instantiates it if the cache is empty.
In case there are still issues with migration process you can share the code that creates the ReportBook so we can test it on our side.
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