Mirena strings encased in cervical tissue?

So during my colposcopy my doctor said she was seeing something she has never seen before and it is not listed as a side effect. The cervical tissue has grown over and basically encased the strings of the Mirena IUD. I have to see a gynocologist to have further tests done and see how they are going to fix it. I can't find any info online and was just wondering if anyone on here knows why this might happen or how they are going to correct it. Thank you all.