saved VOI not allowing new segmentations

Operating system: windwos
Slicer version: 4.11
Expected behavior: saved ROI should allow new segmentations
Actual behavior: saved ROI only allows new segmentations within the area within the saved ROI.

I have drawn a VOI on the liver of a patient. I then exported the VOI as VOI.nfti (clicked on the segmentations, export to files), during which i included the reference volume (which was the CT),
I then closed the slicer, reopened the CT, and re-uploaded the VOI.nifti. the VOI registered well with the liver. However, when I added another segment to the VOI.nifti, I could only draw on the area of the liver (for example the spleen), but not in the lungs.

Please help!