I filed back in March. But today I received an IRS letter claiming that Schedule A, Schedule D and Schedule 1 were missing or incomplete. What happend?

I've used TurboTax for years and never had a letter from the IRS claiming they didn't receive certain schedules. It's strange too because the IRS cashed the check I sent and the state issued me a refund back in March. So, why do they claim schedules are suddenly missing or incomplete?  Could it be a scam?