in order for exports (in WSXZ or other formats) to be processed correctly in the Modern User Interface, the configuration of background_daemon needs to be set in general.properties under WS_CONFIG/ws-api. This configuration will be applied to background processes initiated from the Modern User Interface. This includes exports and imports of WSXZ packages from the Projects and Tasks page in the Modern User Interface.
If such a configuration is not present, the export will not start. The resolution is to make sure that the general.properties file is present under WS_CONFIG/ws-api and that it contains at least a value of 1 for the background_daemon property. For example: