Did a brew yesterday, hit the desired SG after the boil time - or so I thought. After cooling the wort, the SG dropped 2 points. What would cause this?
Your hydrometer has been calibrated to give readings at a specific temperature. Depending on the temp when you first read it and the temp after cooling a two point difference is not that surprising.
If you look closely at the hydrometer, it will tell you the calibration temperature of your hydrometer. They are normally done somewhere around 60, 65 or 68F.
There are hydrometer correction tables/tools available online to help with this in the future so you don't have to wait for the sample to cool. Like this one at Brewers Friend.