Hi Deepa -
Yes, this has been happening with the latest Slicer due to tightening of the ITK file loader in terms of what it considers valid nifti format. (See here and here for some discussions).
What software generated this file? Arguably the file is ambiguous (non-conforming to the standard) and the software that generated it needs to be fixed.
As a workaround you could use the older 4.11 version to convert to nrrd if you don’t have any other options. Or perhaps you can use a different file format from the beginning.
-Steve