How to Fix WP Amelia, Time Options for Booking Disappear / Does Not Show When it is Set for Employee?

This typically changes if you change time interval into a larger number.

Check that in settings the time interval fits the time slot.
For example if your appointment times are:
10:00-10:15
10:20-10:35
10:40-10:55
11:00-11:15

And if Time Interval settings is 30min, then only these time slots will show:
10:00-10:15
11:00-11:15

TO fix, make sure that time interval is set at 5min.