Vanishing twin not yet absorbed at 17 weeks

Hey everyone’s early on the doc found two sacs and at 8 weeks I had another ultrasound where only one heartbeat was found. He said my body would absorb the vanishing twin. At 17 weeks I finally had another ultrasound to learn that the tech found “membranes” still and they have scheduled me for a level 2 ultrasound with a specialist at the hospital for next week at 20 weeks and cancelled my anatomy scan in his office. He said this was nothing to worry about but I can’t help my freak out as to why the level 2 ultrasound. Has anyone had a vanishing twin take longer to absorb and or never fully absorb? And how was your outcome for the viable baby? Doc told me not to google and this was his precautionary to get a better look. But I can’t help but think he just said that to not make me worry! Thanks y’all!!!!