If an incoming web request runs before the configuration is fully completed, you may encounter the following errors in the Management Portal log file after upgrading. These errors are not something to be worried about. They just indicate that the web request was still looking at an old version of the database prior to it being completely upgraded.
2021-11-15 12:41:36.5780 Keyfactor.EF.KeyfactorExecutionStrategy [Error] - Invalid column name 'Immutable'.
Invalid column name 'SubscriberTerms'.
2021-11-15 12:41:36.6249 ASP.global_asax [Error] - An uncaught application error occurred: An error occurred while executing the command definition. See the inner exception for details.
2021-11-15 12:41:37.3281 ASP.global_asax [Error] - An uncaught application error occurred: An item with the same key has already been added.
at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)