I had the same issue for TCEHY entry that had the additional info in 1099 as proceeds from sale of rights. TurboTax was mandating to enter a cost basis as it was blank from the 1099 download for this entry. After talking to a TT advisor over phone they pointed out about the 1099 having info about this gain or loss not reported to the IRS. On a closer look it mentioned that it had to be reported on form 8949 and TT had automatically added this form with the necessary info from 1099. All I had to do was enter the cost basis as 0 and the error got cleared and it didn't change my tax due from what it was earlier.
