UI action condition script returns false or contains syntax errors preventing the button from displaying to the current user or record state. (high likelihood)
User lacks required roles specified in the UI action's Roles field or does not have read access to the target table. (high likelihood)
UI action is not associated with the correct view that matches the form view being displayed to the user. (medium likelihood)
UI action is set to Client=false but the Show insert checkbox is unchecked, preventing visibility on new records. (medium likelihood)
UI action is inactive or the Active checkbox is unchecked in the UI action configuration. (low likelihood)