The social media site's IPO has been steeped in controversy since it started trading last Friday.
Almost a week later, many investors have found that their orders for Facebook were not executed at the prices they thought, said advisers, who declined to be identified because they are not allowed to speak to the press.
All Facebook stock trades in clients' accounts from May 18 have been confirmed, a Fidelity spokesman said.
"On behalf of our customers, Fidelity's senior management has been working with the regulators, market makers and NASDAQ to represent all of our customer's trading issues from May 18, and we will continue to do so until we are confident that NASDAQ has done everything it can to mitigate the impact to our customers," the spokesman said.
Nasdaq had all orders, executed or not, returned to member firms by 1:50 p.m. EDT (1750 GMT) on Friday, according to a trading alert issued by the exchange on Monday morning.
Fidelity, a mutual fund company that also runs a large brokerage, issued a special notice to customers who submitted orders to buy Facebook shares on Friday, saying they may have experienced delays in status updates.
"We realize that some customers still have questions about how these delays may have affected their trading activity," Fidelity said in the notice.
"We understand that Nasdaq is working with federal regulators to determine what, if any, accommodation might be made. However, customers should assume that any shares of Facebook stock currently credited to their accounts are owned by them and available for trading."
Facebook's IPO did not go as planned as its sky-high valuation, combined with trading glitches, left the stock languishing below its offering price.
Fidelity said Facebook order glitches were an industry-wide issue that affected many different broker-dealers.
"We will continue to work with the industry to get NASDAQ to come to a resolution that addresses the concerns of our customers," Fidelity said in the notice.
Boston-based Fidelity has 18.3 million brokerage accounts and reported nearly 396,000 average daily commissionable trades in the first quarter. Most of that activity centered on personal investing.
Facebook's shares gained a penny to $32.01 in midday trading on Thursday.
(This story has been refiled to delete paragraph 13 saying Fidelity not available for comment)
(Reporting By Tim McLaughlin; Editing by Walden Siew and Maureen Bavdek)
By Jessica Toonkel and Tim McLaughlin