The amounts in Box 17 are not used to calculate your income, so nothing is really being added to income. The UBIA amounts are only used to calculate the reduction amount of the QBI deduction if applicable (if you are over the QBI threshold amount).
And the UBIA is an amount used for the calculation of QBI; it doesn't get factored into your actual income reported on your tax return. The Unadjusted Basis Immediately after Acquisition (UBIA) reflects the basis of the property when it was acquired or placed in service, so these amounts could come from asset entries from previous returns.
Code X is needed to properly calculate the QBI deduction. Be careful when overriding data; that could void the Accuracy Guarantee.
See page 2 for a description of the Box 17 codes - https://www.irs.gov/pub/irs-pdf/f1120ssk.pdf
