The current implementation of the WebAPI ReportController requires that is run as a Singleton. When running on Azure with multiple instances, it doenst work well. For deployments with large amounts of HTML reportviewer clients, one report server is not enough, it needs to scale. I suggest putting shared reportcontroller state (resources) in a configurable external out of process multiple concurrent access safe data structure. Solutions could range from database to shared in memory nosql, for instance Redis or Azure cache.