I filed and it was accepted same day on 2/3/20 and I still have not received my refund yet. I received a letter yesterday saying it is under review. What does that mean?

The letter says they are reviewing it to ensure it's correct and that it will be delayed.  Does this indicate I'm being audited, or that they truly just checking it, or is that just a lame way to delay things further?

UPDATE:  I got the letter yesterday and the refund came today.  43 days after filing.