SLA’s it is working fine in the “contract_sla” table. It is correctly showing the breach time for the SLA as well as per the defined schedule.
However in the “task_sla” table in which these are attached to the incident tickets, the breach time not getting calculated even though the schedule is getting populated.
The issue is caused because Script includes - SLASchedule was customized and it was not containing code to set Schedule correctly.
After reverting this to OOB issue is resolved.
Link to Script include - https://<instancename>.service-now.com/sys_script_include.do?sysparm_record_target=sys_script_include&sysparm_record_rows=1&sysparm_record_row=1&sysparm_record_list=sys_idINe754da649f3200008f88ed93ee4bcc45%2C%5EORDERBYname&sys_id=e754da649f3200008f88ed93ee4bcc45&sysparm_nostack=true