Losing sugar?

[Acefisher1]

Using new membranes on a three post cdl unit. Everything ran great, processed close to 4000gal of sap this morning then boiled. I did check permeate with both a hydrometer and a Milwaukee refractometer. Hydrometer sank to 0, refractometer read 0.1 after calibration. After boil, did not end up with nearly the amount of syrup I should have given the sap sugar content. Granted it was the first boil of the season so evap still has a fair amount of sap in it. I know those refractometers are not the most reliable but am I losing sugar and how? Or is what I experienced normal for first boil? Thanks for any input

[maple flats]

On a first boil you will never get as much as tests say you should unless you completely finish off the contents of the pans. On my 3x8 sending 10% concentrate into the float box, I can boil for almost 2-2.5 hrs before I get my first draw. After that it is fairly steady. There's a lot of sugar in the pan, the bigger the pan, the more sugar is in it until your final boil.