Yep. 27 is 1 PSI less than 28. We have been presuming that you have a submersible pump (down the well). If you have a jet pump, say so.
I presume you now that your pump kicks on at 30 PSI and off at 50 PSI. How long does the pump run each time, minimum?
After your changes, your system worked most of the time, but then it doesn't on occasion. This could occur when there is a bigger demand than usual... perhaps your backwashing filter was backwashing while you turned on a faucet or something. So the pressure tank ran out of water before the pump delivered water. The pressure dropped to 20 PSI momentarily, and the switch kicked off. Letting out 1 PSI of air may totally cure this for you.
A better solution, if the dropping of the precharge a bit does not work, would be to use a basic pressure switch but to have a device that detects a pump running dry. It would then shut off power to the pump for a programmable interval. It works by monitoring the pump power wires, so it could be located anywhere in the path from the breaker to the pump system -- even next to the breaker panel.
Until you do a better solution, you might make a stick with a nail or cog on the side to operate the lever to lift the lever from up top. That will get old fast, but so will climbing into the pit every week or so.