It is possible that salt or iron residue on the probes is the cause. My sump has a tethered float but I have probes for a high water alarm that may at times false alarm. I did two things... one was to clean the probes with WD40 and the other thing was to pipe a vent to the pit to lower the humidity.
You might try waxing the probes to repel water. You could also contact Switch Genius tech support to see if there is any way to reduce the sensitivity or if the unit is out of spec.