Some Technicians report that they are unable to log in to the Salesforce Field Service...

To provide access to the Salesforce Field Service Mobile App, the user’s profile must have the Field Service Mobile permission enabled.Updating Public Group membership, assigning a Field Service Mobile License to the user, or modifying the user record would not grant access to the mobile app. References:https://help.salesforce.com/s/articleView?id=sf.fs_mobile_app_permissions.htm &type=5