Important note when uploading multiple files – Sharepoint prohibits files which have some “special characters” such as & or # in the name. If you try and drag and drop a large number of files onto your site without first checking for special characters, you’re likely to get upload/sync errors.
To avoid uploading files to your site one-by-one in a browser, you have a few options:
1) OneDrive for Business (recommended) – The easiest way to upload a large number of files to your site is to first sync the destination library with OneDrive for Business, and then drag the folder you want to upload to your local Sharepoint folder. OneDrive for Business will then take care of the upload for you.
2) Open your site in Internet Explorer, and use the “Open With Explorer” button on the Library tab of the ribbon. This will open your site as a folder to quickly drag and drop files to.
3) Drag and Drop in browser – when viewing any document library in the browser, you can drag and drop multiple files (although not folders) into the browser to upload them.
