From your description (your file with the same LUFS is smaller in width than the original) I think the issue is your audio file is too compressed.

If the original audio is too compressed, the only way to reach a target LUFS of 14 (for example) is to reduce the amplitude of the entire track.

Watch this video (link originally provided by Tony) that demonstrates this in action.

Skip ahead to around 4:00 or so where he shows the two files and then later when he shows them with the same LUFS: https://youtu.be/n1Yfl6KGRk8