Avada provides this guidance for troubleshooting the demo import process – https://theme-fusion.com/documentation/avada/demo-content-info/import-all-demo-content/#troubleshooting and this additional guidance for when the demo import fails – https://theme-fusion.com/documentation/avada/knowledgebase/what-to-do-if-xml-import-fails/
Your new Avada license comes with 6-months of support included, so best choice for you (IMO) would be to Submit a Support ticket and ask the Support Team to look at your site. You could try the alternate demo import method outlined in the Avada Docs (https://theme-fusion.com/documentation/avada/demo-content-info/alternate-demo-method/). You might also try importing/removing one of the other demos to test the import process. You might also try importing the theme in smaller pieces (it’s a feature on the demo importer – selective incremental import). All of the classic demo pages (actually page templates from ALL the demos) are in your Fusion Builder’s Library Demo page templates without needing to import the demo. Importing a full demo isn’t as big a deal/as necessary to get going with the theme as it was with earlier versions.