The explosion in ETFs since the flash crash, now numbering 1,614 versus 950 five years ago, is another factor in the SEC's decision to take another look at the rules. The amount of investor dollars in ETFs has more than doubled to $2.1 trillion from $826 billion, according to Lipper.

Poring Through The Data

One post-2010 rule, called Limit Up Limit Down, prevents stocks from trading outside of a specific range based on recent prices, pausing the stocks when trading occurs outside of its limits. The rule was applied in 2013 to ETFs, which are securities that track indexes, commodities, bonds or baskets of securities, and trade like stocks.

One of the issues from last Monday was that when the market opened, many stocks were halted or their openings were delayed as the market tanked, making it difficult to properly price some ETFs that had the halted stocks as constituents.

The SEC has long been aware that Limit Up Limit Down affects ETFs differently than single stocks and has asked the exchanges to suggest adjustments to the rule to help smooth out its effects by October, said Steve Crutchfield, head of exchange traded products at the New York Stock Exchange.

"Everything is on the table," he said in terms of the potential adjustments to the parameters of the program, which would have to be approved by the SEC.

Humans Vs Machines

The SEC is also looking at the long-standing differences between how the NYSE, owned by Intercontinental Exchange Inc., and the Nasdaq open the stocks listed on their exchanges during times of market stress, the source said.

NYSE, unlike other exchanges, which are nearly fully automated, uses people on its trading floor to open its stocks, a process it says gives it greater stability because the traders can intervene in ways that algorithms cannot.

But rivals say that using humans rather than computers caused undue delays in opening some stocks and ETFs after they were halted last Monday, intensifying ETF pricing issues.