What solution did you use to calibrate the probe? It shouldn't be the same 35ppt solution to test/calibrate a refractometer, it should be a conductivity solution
like this. Also, it usually takes conductivity probes a couple days to settle in.
When buying a refractometer, look for one that measures seawater and not a brine solution. Veegee, DD Ocean, etc are all "seawater" refractometers. If you paid $50 or less for yours, it's probably not a good one. Tropic Marin glass hydrometers are great and swing arm hydrometers are horrible at reading proper salinity, as they only measure specific gravity, which is temp based.
Also, we should all be measuring (or referring to) salinity in parts per thousands, 35ppt, not specific gravity, 1.020 etc. Specific gravity is temperature related, thus the reading will actually be different based on your water temp, whereas salinity will always measure properly no matter what the temp is. The glass hydrometers will work better, as they are calibrated (usually) for 77 degrees, so one or two degrees doesn't throw it off much.