When uploading large files (several hundred MB) to a SharePoint mount, the progress indicator shows the amount of data being transferred for each file is twice what the actual file size is. Once the 2x file size has been transferred, the transfer starts again from 0. Sometimes, after this "second" upload is complete, the file has been successfully copied up to SharePoint. Larger files, though (1GB or larger) fail completely (they never make it past the initial 2x upload attempt).
Note: using WebDrive on a Windows 10 system.
This issue should be resolved with the most recent version of WebDrive 2017.