You may have an import metadata preset that's clearing the GPS field. To quickly troubleshoot that, in the Import window's right-hand column, make sure that Apply During Import > Metadata is set to None:
If that fixes the problem, then you'll have to edit the preset you were using and make sure it isn't clearing the GPS fields.
If that doesn't fix the problem, then upload to Dropbox (or similar) a sample pic that hasn't yet been imported into LR. Post the link here, and we'll take a look at the pic's metadata.