The Access Digital Assistant determines priority only when a ticket is first converted from a conversation, so a ticket that grows in impact needs updating by hand. Recalculate the service level straight afterwards, or the timings stay on the old priority.
Change the priority
To update the priority and the service level together, work from the ticket details.
Click Details, then click Conversation attributes.
Select the new level in the Priority field.
Click the reply box, then select the Trigger Reusable workflow shortcut.
Select Recalculate SLA.