my sister and I recently applied for AP on humanitarian reasons. I was approved in about 2 weeks but my sister's case cannot be tracked online/over the phone.. should I be worried?

Timeline:
- both applications mailed and received by USCIS on 3/8
- received I-797C notice of receipt on 3/11 (for both my sister and I)
- I was able to track status of my case online but my sister's case number gives "validation error"
- my AP was approved and I received the AP documents on 3/25 (super fast!)
- no update on my sister's app till this date, still says validation error online...