The New York Stock Exchange experienced a "critical" technical issue Wednesday and suspended trading on 199 ticker symbols.

It was the latest in a series of issues affecting one trading unit with the same symbols. Trades in the affected symbols continued to come through other market centers.

Both the Nasdaq and BATS stock exchanges had declared self-help against the NYSE amid the multiple technical issues that closed all open orders on the symbols. A self-help exception allows trading centers to bypass an automated trading center that is experiencing system problems, according to the SEC.

NYSE believes the stocks affected are traded by Citadel KCG at Post 5, said NYSE spokesperson Kristen Cause. The area of the trading floor was roped off as the issue was addressed.

Cause told CNBC that she believes the issue is linked to the NYSE's own system but it will continue to look for the root cause.

Tickers like the Bank of Montreal and Agilent Technologies were affected.

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