Rescheduled appointment canceled an existing appointment

Today I had 15-minute meetings scheduled at 3:30 and 4:45. At about noon, my 3:30 appointment rescheduled to 4:30. This should have been fine, but when they rescheduled for 4:30, it seems to have automatically canceled my 4:45 appointment. So far as I can tell, the only reason for this is the 5-minute buffer I have on before meetings. Can someone please explain to me how this happened so I can prevent it from happening again?

Also, I see numerous posts on this forum (going back 2 or more years!) requesting the option to restrict the rescheduling options. I want 24 hours notice before any meeting so I can confirm my schedule, but if someone is able to reschedule an appointment to 2 hours or even 30 minutes from now, how am I supposed to ensure that I am available? Can Calendly please add in the option to prevent someone from moving one of my meetings to a time that I am unable to prepare for?