The date after unavailable day is unavailable

When I choose my availability, if I set May 5th unavailble, it appears red, and May 6th appears green. All good. But if I click on May 6th in the calendar, even though it is green, I get an error “It appears you have selected an unavailable or invalid date. Please refresh the calendar and try again.” It does this to every “day after” an unavailable date. What can cause this? Thank you!