A: Yes. Boveda, makers of the humidity packs you find in some cigar boxes, also make a “One Step Calibration Kit.” Since it appears you’ve done the salt test correctly, my gut tells me the hygrometer is most likely bad; in which case, don’t spend any more $$ unless you want to try one more possible solution.
Purchase the calibration kit, remove all the cigars from the box, and keep them safe in a ziploc bag. Since you can’t remove the Vision hygrometer without a lot of difficultly, just place the Calibration bag open in the empty Sensi-box and keep the humidor closed for a day. If you get similar, low RH readings, or the RH does not move at all, it should prove your salt test was correct and the unit is bad.
The best way to go would be to purchase a new digital hygrometer that will fit comfortably inside the box and a Boveda Calibration Kit. The new unit should be more reliable, and you won’t have to deal with the factory hygrometer at all.
Finally, use the calibration kit on your new hygrometer before you place it in the Sensi-box. (The kit can be used repeatedly for up to 90 days.) Then, unless that one is also bad, you’ll have a much better idea of what the RH really is, and you’ll sleep better. too.