Realm fetch from a class doesn't work the first time

The below code doesn’t run first time, but when I close the app and re-open it, it works.
Could someone please explain why this is happening

class Singleton {

    func observe() {
        guard let config, let user_id .... 
       let realm = try! Realm(configuration: config)

       let mee = realm.object(ofType: Person.self, forPrimaryKey: user_id)	 
       // is nil first time I run it, even if data proper exists
        guard let meeee = mee else {
	        print("incomplete USER")