If your refund is short $1,400 then the IRS has records that show you were sent the 3rd stimulus payment so they removed the $1,400 Recovery Rebate Credit that was entered on Form 1040 Line 30.
Go to this IRS website for your tax account to see if the 3rd stimulus payment is entered - https://www.irs.gov/payments/your-online-account
If you checked your bank account in the March - May 2021 timeframe and there is not a $1,400 EIP3 payment from the IRS then go to this IRS website for how to start a trace on the payment - https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-p...
