Same thing happened to me.
I don't weigh myself that often- once every 1-2 weeks. I bought my new digital scale last month I was so upset the first time I weighed myself thinking I gained 4 pounds! Then I got back on my old scale and I was 4 lbs lighter. So I was actually 4lbs heavier when I started! I went and readjusted my start weight and current
but I guess I still lost the same amount-they're just numbers