The reason is if you “shutdown” does not actually shut down most of the time in Windows, but only hibernates.
Unmount the Ntfs partition by running
sudo umount -a
to get the partition to mount with full read/write access
sudo ntfsfix /dev/sdaxx #(for example /dev/sda3)
References
https://superuser.com/questions/1394263/ntfs-file-system-read-only-by-ubuntu-remount-doesnt-work