Its unpredictable
allaboutgc,
Usually an email from USCIS always coincides with a LUD change. Sometimes this does not happen. When an RFE was issued on my wifes 485, the LUD changed for a couple of days then we received an email stating that some more information is required and finally the LUD message changed to what the email stated on the same day.
Hope this answers your question. What is important is to make sure your lawyer gets the RFE and that the lawyer responds to it in a timely manner.
regards,
saras