There is no size limit but if the number is more , you may see the move operation is unsuccessful msg but when you will validate the assets or folder may be there but this is not a consistent way of moving a large no of assets. Happened with me on AEM CaaS . Ideally, you should be using ACS AEM Commons tool https://adobe-consulting-services.github.io/acs-aem-commons/features/mcp-tools/renovator/index.html for the bulk move operation . Also , depending on no of assets moved you may want to check if you want to disable dam update workflow and run it later in batches to optimize author performance . Hope this helps.
Also , if not the 'admin' user directly , you can double check on the user's unpublish permission and check if issue is specific to moving assets that are published.
If AEM is AMS/On-premise - do check logs/resources (disk space/memory). You may need to run OTC/GC if issue with resources.