If a caller agreed an appointment more than about a week away, it was dropped on the very next thing they said. They would agree a time, give their email, and be told “sorry, that is no longer available” — then offered times for today instead. Nothing had been booked by anybody else. The appointment was never taken; your receptionist had simply stopped being able to see that far into the diary when it went back to check.
The further ahead the appointment, the more certain it was to happen, so it hit exactly the bookings people plan around — and it hit businesses with longer opening hours hardest, because more appointments a day meant it could see fewer days ahead.
What happens now. Your receptionist looks further into the diary before deciding anything, so an agreed time stays agreed for the rest of the call. A time that genuinely has been taken by somebody else is still reported as taken — we test both, because a fix that simply never said “taken” would be worse than the problem.