Typically with an issue like this, we need to be able to view the log and the settings. In order to do this, we need support access enabled. Opening a ticket with support is the best course of action.
I will take a guess here. Please check what version of Xcode Archive you are using. This step was recently updated and a new version, version 4, was released. This new version changed the name of the step input for the export method and set the default to “development”. If this step was updated in your workflow, please check the value for “Distribution method” to see if it is correct.