Im so lost right now.

I went last week for ultrasound (5w) 2 sacs clear as day. No heart beats yet. Went back today measured 6w3d. And still 2 sacs clear as day but one heart beat. We were so excited for 2 babies. But now they are saying probably vanish twin syndrome since other sac is still empty. I read so many stories that some produce later then the other twin. But idk what to to think anymore. I'm lost. Someone give me some insight. My next ultrasound is jan 4th at 9 weeks