Several rail firms reported problems with pre-paid ticket collection from machines across the country on Tuesday morning.
Greater Anglia, Thameslink, Stansted Express, Southern, Southeastern, and ScotRail all confirmed they were affected by the issue.
The Rail Delivery Group, representing train operators, said the problem was fixed at around 10:00 GMT.
Customers were advised to use staffed ticket offices where possible.
Most rail companies had said any proof of purchase, such as a ticket reference number, was being accepted instead.
One person tweeted that the button to collect pre-paid tickets was greyed out on "every machine" at London Liverpool Street on Tuesday morning.
❗ We have been made aware of an issue regarding collection of pre-paid tickets from some ticket machines across the Greater Anglia network. If you are unable to collect your ticket, please travel with your ticket confirmation email. GA— Greater Anglia (@greateranglia) February 19, 2019
A spokesman from the Rail Delivery Group said one of the suppliers of the ticket machines had been experiencing problems receiving information from computer servers.
He apologised for the inconvenience caused to passengers and advised those affected to speak to their train company or visit their ticket office.
He confirmed the issue had affected multiple operators but not all machines across the country.
The issue only affected the collection of pre-paid tickets, and all other ticket types could be bought from the machines.
Virgin Trains said its ticket machines had not been affected.
Earlier, rail passengers had been turning to social media to vent their frustration.
Gayle Gorman tweeted: "@scotrail no ticket office open / ticket collection machine not working at Stonehaven! So much for pre planning!"
Good Morning and welcome to #Crayford station:— Lewis Glynn (@lewisglynn69) February 19, 2019
- Our ticket office is closed
- Our ticket machine doesn’t accept card, cash or Oyster cards
- Our electronic timetables are broken
Have a great day, love from @Se_Railway #southeastern #TrainTraveller
Matthew Farren, tweeted: "Well done @tfwrail Not only is the door to get into Newport station not working, but now the ticket machines are broken too - doesn't inspire a great deal of confidence."
Rail passenger Eleanor Mason warned other travellers: "If you've booked train tickets for collection leaving Shrewsbury train station today give yourself plenty of time as both ticket machines this morning aren't allowing you to collect (and there was only one person there this morning so be prepared to queue)"
If you’ve booked train tickets for collection leaving Shrewsbury train station today give yourself plenty of time as both ticket machines this morning aren’t allowing you to collect (and there was only one person there this morning so be prepared to queue) 🙄— Eleanor Mason (@Eleanor_L_Mason) February 19, 2019
Rail ticket machines also fell out of service last June, with on-screen messages saying there was "no online connectivity".
The issue, which was resolved after three hours, appeared to have originated from the software and systems provided by Scheidt & Bachmann, but the German firm did not provide additional information.