No it isn't normal. We know they have your address correct, because you got the biometrics notice. That's good, because it means you have the receipt/case number if not the notice. You can call customer service with the receipt number to request the notice be re-sent. The receipt notice is more important in this I751 situation than in other cases, because in the 751 situation the receipt notice extends status for a year. In the alternative, get a good experienced immigration lawyer.
This reply is intended only as general information and does not constitute legal advice in any particular case. This reply does not create an attorney/client relationship.