Uploading large files or many files to a document library
If you are uploading large files--or many files that add up to a large total size--to a document library, you may get errors due to the file size limit in Office 365 and SharePoint Online or timeout errors in your version of Internet Explorer. Steps you can take to get around these errors include:
Upload 100 or fewer files at a time when using drag and drop.
Avoid uploading files larger than 2 GB for SharePoint Online.
For file sizes exceeding 2 GB for SharePoint Online, if you see a "Working on it" message that never goes away, follow the instructions in Microsoft Support: Internet Explorer error "connection timed out" when server does not respond..