Workflow attached to SLA through Custom BR not considering the retroactive start.
Retroactive start is triggering notifications for already existing activities
Most Probable Cause
Workflow which got triggered on the task sla through the custom Business Rule has no connection with the SLA definition and that's why it's not considering the retroactive start and it's working based on the new start time.
If you want to stop the notifications, you can disable the property as mentioned in the product documentation when retroactive start is set: Use SLA retroactive start and pause.
When retroactive start is enabled, it may result in task SLAs being breached as soon they attach, which will trigger multiple notifications. To prevent the workflow from being processed for these breached SLAs, set the com.snc.sla.workflow.run_for_breached property to false.