I am having the same issue for my deceased father's tax return. I had to file on paper as I needed to prove that I can claim it or fill out the form 1310. I included the original certificate of administration that allows me to claim his refund. The refund is the rebate credit btw.
According to USPS, they received it on March 10. I don't know if "where is my refund" cannot provide information because I enter deceased's SSN or because they lost the tax return including my original letter of administration from the surrogate court.
