Many users have reported that they have received USCIS case status updates which says an action was taken on the case but they could not see anything new once they logged in to USCIS website. There is no clear explanation shared by USCIS. But, users have reported that the status does get updated in about 1-5 days after this email/text notification. Usually, the action is in the form of approval, denial, RFE or biometric appointment notice issued. You will get a paper mail too for this USCIS action.