@nhhchang From this IRS website - https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue
The IRS is opening mail within normal timeframes and all paper and electronic individual refund returns received prior to April 2021 have been processed if the return had no errors or did not require further review. As of February 18, 2022, we had 8.1 million unprocessed individual returns. This includes 4.3 million unprocessed individual returns, which include tax year 2021 and prior returns with errors and those returns requiring special handling such as those that require correction to refundable credit amounts. This work does not typically require us to correspond with taxpayers but does require special handling by an IRS employee so, in these instances, it is taking the IRS more than 21 days to issue any related refund and in some cases this work could take 90 to 120 days. If a correction is made to any Recovery Rebate Credit, Child Tax Credit, Earned Income Tax Credit or Additional Child Tax Credit claimed on the return, the IRS will send taxpayers an explanation. Taxpayers are encouraged to continue to check Where’s My Refund? for their personalized refund status and can review Tax Season Refund Frequently Asked Questions.
