MS Case : 17052664 >> Post upgrade of SCCM CB 1906 we realised that one of remote SMSPROVIDER server was not working properly. This remote SMSPOVIDER never had ADK installed on it since SCCM infrastructure was setup. Error never reported in the past in any upgrade but it stopped working post successful upgrade of 1906. In order to fix this issue in future it should be part of Prerequisite check in upgrade setup.