you can tell what it is on the website. it’s probably just a RFE but login and see the status there

you can check it under your documents tab and see what they are asking. That will explain what they are looking for and it’s completely normal. No need to worry

mine was for medical and I have responded since August,they acknowledged receipt on 4th of September instead of 16th of August that they got it. I am still waiting for their decision. It is nothing serious,just make sure you respond accurately