Date filter going back to 1899

I have created a custom column based on this query, however,  the column shows date all way bak to 1899 even though my data doesnt have any date going that far. does anyone have any suggestions on what the issue might be ?

COLUMN =
IF (
    (
        [ACT_START_DATE] <> BLANK ()
            && [ACT_END_DATE] <> BLANK ()
    )
        || [ACT_START_DATE]
            <= TODAY () + 2,
    [FINISH_DATE] - 1
)