There are several posts explaining why there's a delay.
You could also check the IRS notifications regarding the issue.
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The IRS is reviewing the tax provisions of the American Rescue Plan Act of 2021, signed into law on March 11, 2021. Taxpayers who filed a 2020 tax return and reported an excess advance premium tax credit repayment on Line 29 of Form 8962, Premium Tax Credit, should not file an amended tax return only to get a refund of this amount. The IRS will provide more details soon. For the latest updates, check IRS.gov/coronavirus.