Any ladies have their IUD's go ghost?

Had an appointment today to remove my Mirena after having it for 8 months. Was so excited because hubby and I are ready to TTC. Doc couldn't find the strings 😑 I was wondering how normal this was or if anyone on eve had a similar story. No unusual pain, other than the first 2 weeks of insertion. I have a pelvic ultrasound on Wednesday. Let's  hope they find that sucker!