Have a newer Otis 211 5 stop with 1 short floor. Unit is set to park at the lobby floor. At least once a day, it shuts down. There is no shutdown code shown, display shows OK at shutdown code menu. Display scrolls run 187, 365. 3NAV. I know the numbers are just counters and NAV is not available. When I reset, I see the floor number scroll and several upside down exclamation points follow. Then it will take right off again. Without a shutdown code, I'm flying blind. Any help will be greatly appreciated.