We've removed those as default escalation actions for the case-level SLA starting in 7.2.1 to eliminate this very common point of confusion that we introduced by sharing common escalation actions for both the case-level and step-level SLA.
Notify assignee and Notify manager escalations actions are only designed to be used for step-level (i.e. assignment) notifications. What you are showing in the screenshot appears to be the case level SLA. For each step in your case life-cycle you can add a SLA where these default actions will work properly. If you require case-level esclation actions that notify specific users, you will need to configure the case-level SLA rule directly in the Designer Studio.