Hydrometers are calibrated at different temps. Believe 60F and, I believe, 68F. Sure you are using the correct calibration temp for the new hydrometer?
Malts. Malt analysis changes. Just because a certain malt produced a certain gravity last time is no guarantee a new batch of the same malt will do the same this brew. Also, malt with same name from different maltsters have different specs. Brewing software relies on the malt specs in the software. Unless one has changed the brewing software malt specs to match the current malt specs this may account for differences (estimated vs actual).
Mention the mash temp. I was just getting ready to ask about differences in mash temps. Any way to insulate the kettle to keep the temp at or near the desired temp (in this case 150F)?
pH? How is the water pH? Has the water pH changed since getting higher efficiency?
Too quick sparge. Has the sparge time changed since getting the higher efficiency? Quick sparge, while good for us (meaning saving time), really is bad for extracting fermentables.