Decarbing gone wild

im wondering why m losing thc potency. we decarb at a ten to 1 ratio e
200 proof ethanol extraction threw a rotovape btw.about 2000 grams at a time usually,went from 90 percent to 75 percent without hanging any method so i guess my question is what would be the most common factor.qaulity of trim? to much carbon or is the testing facilities full of shit