1120S, Line 21, does flow to Sch K, Line 1.
Did you check whether you have entered any adjustments/override? In the first instance, you may like to take a look at Ordinary Income > Schedule K > Income and Deductions, particularly on the line Ordinary business income (loss) [Adjust]. You may also like to type the amount you see on Sch K, Line 1, in the search box and see whether there is a hit under Field Data.
If no override/adjustment is found, there may be a problem with your return. Your best bet then is to send the return to Support and have them look into that on the back end.
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