If you just copied 1TB of data onto the drive, and your files included a lot of photos (placed into the Shared Photos folder), then the MBL may be making thumbnails for the WD Photo mobile app in the WD Photo Database.
If you do not want to use remote access, then you can uncheck the Enabled option of Remote Access and the activity should top. You can also prevent the thumbnailing by putting the Photos in a different folder, not the Public\Shared Photos (may need to be in a different share instead of Public?), but then the WD Photo app will not work. If you want to use the WD Photo mobile app, then you will need to wait for it to finish (the time required will depend on how many photos you have).