If the decedent was alive in 2020 then they are entitiled to the stimulus money on their final return. https://www.irs.gov/coronavirus/second-eip-faqs#Eligibility
So it sounds more like a data input error by the user ... the taxpayer should verify that they did not get the money and if the IRS is wrong they can have a trace put on the missing check. https://www.irs.gov/coronavirus/second-eip-faqs#paymentlost
