Not entirely sure what’s happened,
but my guess is you have ‘custom split normals’, maybe when recalculating normals you may have pressed merge by accident.
Below the nomals drop down where you enable auto smooth, you will see a Geometry Data dropdown, here you will see three buttons to clear different geo data, they should be greyed out, if the ‘Clear Custom Split Normals Data’ is not greyed out, the words are white, click this to clear, and your shading should return to normal.
Hope this helps.
