The Federal Reserve is investigating the second significant disruption in 2019 of a payments service administered by the U.S. central bank. Certain bank transactions were delayed Thursday after the Automated Clearing House system (ACH) experienced problems. The system is now back up and running.

"ACH is operational," said Jean Tate, a spokeswoman at the Atlanta Fed. "There was an internal processing issue that delayed delivery of some files this morning. Technical teams are investigating the root cause of the issue." The Atlanta Fed hosts the central bank's Retail Payments Office, which processes ACH transactions.

The ACH system handled 58.5 million transactions a day, on average, in 2018, with an average value of $1,760.

Earlier on Thursday, several banks tweeted that they were experiencing issues.

A Fed website dedicated to the central bank's payments processing services posted a notification at 9:57 a.m. on Thursday saying: "The FedACH Services application began experiencing a disruption on December 18 at 3:30 p.m. Payment files and acknowledgments are flowing as of 7:40 a.m. on December 19. Federal Reserve Bank technical staff continue to investigate the issue."

Spokespersons at the Fed's Washington headquarters didn't immediately respond to request for comment on the issue.

This marks the second disruption to a Fed-run payments service this year. On April 1 the FedWire interbank funds transfer service went down for about three hours. The Fed blamed the outage on "an internal technical issue" but declined to provide more details.

Bloomberg News sought additional information about that outage under the Freedom of Information Act, but the request and a subsequent appeal were denied by the Fed Board of Governors.