case milestones not visible on record

There could be several reasons that a Milestone may not show:

• The Case must have an Entitlement on it. To do this, the field 'Entitlement Name' must be populated, usually with an Entitlement on the Account related to the Case. This field is 'Hidden' in Field Level Security by default, and is not on the default page layout. So the page layout must be customized (https://help.salesforce.com/articleView?id=customize_layout.htm&type=5&language=en_US) in order for this to work, and field level security for this field (https://help.salesforce.com/articleView?id=users_fields_fls.htm&type=5&language=en_US) must be set to 'visible.'
• The Entitlement needs to have an Entitlement Process associated with it. Go to the 'Entitlement' on the Case, and check for the 'Entitlement Process' field (https://help.salesforce.com/articleView?id=entitlements_fields.htm&type=5&language=en_US) to be sure that there is a value there.
• The Case must qualify for any of the defined milestones, as per Milestone Criteria on the entitlement process (https://help.salesforce.com/articleView?id=entitlements_milestone_adding_sla.htm&type=5&language=en_US).