This behavior appears to be due to the record associating 'SAG - 8-6 weekdays excluding holidays - UK' with the child record 'SAG - Holidays - UK'.
Using the schedule entry 'Good Friday 2018' as an example, the entry appears to be created correctly. For this particular record, the Type should be Excluded (which it is). However, for the record mentioned above, we will want to use the Include value. I believe when this is set to 'Exclude' we are not associating the records from schedule 'SAG - Holidays - UK' to schedule 'SAG - 8-6 weekdays excluding holidays - UK'. So, the entries for the schedule 'SAG - Holidays - UK' look correct, we just need to ensure they are associated to schedule 'SAG - 8-6 weekdays excluding holidays - UK' by updating the Other schedule record to Include. This should prevent the behavior being seen in the future.