I had same situation with sponsor. In my situation they asked W2/1099, then proof of income, then evidence of income. I submitted next documents and take DQ after four attempts
letter from sponsor ( print letter, sign it and scan in color) with explanation all details and attache maximum proof
proof of income - take notarised deposit account balance summary in bank on paper
evidence of income ( statements from bank account, where they can find information about income, take statements not only 2019-2021 also you need for last 60 month any contracts and etc.).
IRS Transcript for every years, its better then Tax Return.
then you upload any document, write description in note. Maybe they didn't want search and think.