8.84K viewsOPTOPT stem

I was asked for a request of evidence by USCIS for my STEM OPT extension is it normal that this would happen if not what would have been the reason for this kind of status change on my application.
I did not get mail to my home but it says they have posted it today and will receive it in a couple of days
but for now i just wanted to know that does this actually happen to any one i am a bit worried
everything is right about my filing i even dont have unemployment period problem