Cost basis may be reported as "N/A" for one of the following reasons:
Stocks purchased prior to Jan. 1, 2011, mutual funds, ETFs purchased before Jan. 1, 2012, are noncovered securities, these will not have cost basis. Your tax advisor will be able to assist you reporting gain/loss if these securities positions are closed.
Positions transferred to Firstrade from another broker without any cost basis information, will not display cost basis.
Short Options: Starting in the 2020 tax year, the closing of short option positions will be reported on Form 1099-B.