I got a check from the IRS in October that was unexpected. It said "We apologize for the inconvenience but we made an error on your 2018 Form 1040. To correct our mistake, we adjusted your Schedule D. As a result, you are due a refund of $x,xxx.
Did the IRS make a mistake or did I?
If you filed early and had Schedule D for investments or sales in your return the IRS had an update and has been sending refunds or tax due bills.
IRS info on Schedule D changes (after May 15, 2019)