I was flying around today and noticed my VPS was having errors. I did all the calibrations like I always do. I started up on flat surface. When the bird first launched everything was ok. I live in Florida so there are no hills/mountains. As I was flying I noticed my height was at -21.5 feet and I was hovering 10 feet above ground.. I then decided to land it. Turn off the bird reset the dji pilot app. Put the bird back up in the air and everything seemed fine. I started flying again and noticed as the bird was hovering near me about 10-15 feet in the air once again the height was off and said I was .3 ft above. Not sure whats going on but I took a screenshot and you can clearly tell the bird is above me on flat grass and the height is off. Any advice?