Losing muscle rather than fat

I have lost 35 pounds and am at my goal weight of about 137. At first I was pretty good at losing body fat, according the the computer scale my personal trainer uses. But at the 145 lb mark, I began to lose only muscle mass despite eating more protein. That is 8 pounds of lost muscle and my total body fat is still 33% which seems high for someone who is a size 6/8 (5’7″). Of course, I feel great and thin and only worry that losing muscle mass will mean I burn fewer calories and make it more difficult to maintain this weight. Is this concerning? Do you think these scales really work?