What's probably going on is that, when TurboTax asked you about the stimulus payments that you received, you said that you did not receive the first stimulus payment of $1,200.
If it's true that you did not receive the payment, then TurboTax was correct to include the Recovery Rebate Credit on your tax return.
If you actually did receive the payment, but you told TurboTax that you didn't, then your incorrect input caused TurboTax to claim a credit that you are not entitled to. The IRS knows what stimulus payments they sent to you. If they sent you the first stimulus payment, but you said you didn't get it, they will adjust your tax return to remove the credit and reduce your refund.
I believe the IRS is manually checking all tax returns that claim the Recovery Rebate Credit, so that can delay your refund.
