Actual elapsed time and Business elapsed time for a task_sla record are showing a value of zero seconds.
Jakarta Patch 7
This is expected behavior for a SLA which attaches in a paused state and moves immediately to Completed/Achieved.
To verify that the affected task_sla record was paused, be sure to add the "Pause duration" and "Pause time" fields to the task_sla list view.
The SLA definition "Priority 1 - High SLA" attached after the previous similar task_sla completed. However, it attached in a paused state. From its attachment on 09-02-2018 20:48:01, to 07-04-2018 20:00:20 (when the incident was moved to a state of "Closed", thus fulfilling the stop condition of the SLA definition - moving this SLA to "Achieved"), it was paused for 56 days 23 hours and 12 minutes.
When an SLA definition attaches in a paused state, it does not accrue time as some might expect. Both the "Actual elapsed time" and "Business elapsed time" will remain at zero as the task_sla is paused.
As this task_sla did attach in a paused state, and was only "unpaused" when it's stop conditions were met and it was moved to "Achieved" (some users may see this as "Completed"), that explains why both values are '0'.