microsoft bookings

Hi,

I set up multiple services in the one calendar for different meetings but with the same time slots. When testing there was no issues with the time slots. I had set 9:30, 11:00 and 2:30. But once the bookings went out to Customers, some of the services created new additional time slots like 11:30 and 1:30. Each of the services had the same set up for availability. Default scheduling policy was turned off and each staff on the calendar had sync with Outlook turned off also. Duration was 2hrs and Time Increments was 150 mins. Why did some of the services create new slots while others didnt and how can I prevent this from occurring again.

Kind regards,
Senan