IRS Letter States "No Record of Processed Tax Return" Though I Filed in February - What Do Codes 570/971 Mean?

I've been staring at my transcripts for hours and I'm completely lost. I filed back in February and my refund still hasn't shown up. Can someone explain what all these codes mean? I see a bunch of numbers like 570 and 971 but I have no idea what they mean or if this is good news or bad news for my refund. I received a letter from the IRS (from PHILADELPHIA, PA 19255-1498) with Tracking ID: 107358545591, dated 01-31-2025. The letter states: "Information About the Request We Received On January 31, 2025, we received a request for verification of non-filing of a tax return. As of the date of this letter, we have no record of a processed tax return for the tax period listed above." The letter also says "If you have any questions, you can call 800-829-1040." This is really confusing because I definitely filed my return in February. How can they say they have "no record of a processed tax return"? Does this mean my return was lost? Does this have something to do with those 570 and 971 codes I see on my transcript? I'm worried because I was expecting a decent refund and now I don't know what's happening. Has anyone dealt with this "verification of non-filing" notice before while waiting for a refund?