NatWest has apologised to customers after its online banking and mobile app were hit by a glitch for more than eight hours during the Black Friday sales.
On what was also payday for some people, being the last Friday of the month, customers complained about being unable to access their money.
Some also said that money they had transferred between accounts appeared to have vanished.
The problems were reported from just after 9am on Friday and NatWest said the issue had been resolved at 5.30pm.
NatWest said the problems affected access to mobile and online banking and there was no impact to debit cards, credit cards, ATMs, telephone and branch banking services.
A spokesman for the bank said: “All our services are now operating as normal. We apologise to customers for the inconvenience caused.”
Earlier on Friday, Twitter users had vented their frustration at the latest problems – with some saying they were unable to see money in their accounts.
One said: “Shocking online banking down again on a Friday. After 10 years of using you I’m fed up of this I’m changing banks now.”
Another wrote: “Transferred my pay day money over to two different accounts and now I have nothing.”
And another said: “I’m getting statements my #natwest transfers have gone in but no actual money on my bank balance.”
Another Twitter user said they were actually saving money on Black Friday due to NatWest’s services being down, writing: “I’m saving tons of dosh because #natwest is down.”
Research from Which? released earlier this week found the banking industry suffers around five IT failures each week typically, shutting millions of customers out of accounts and making payments.
Which? found that over the past year, major UK banks suffered 265 IT shutdowns between them that prevented customers from making payments.
TSB recently apologised to its customers after some account holders were left without their salaries as the bank failed to process overnight payments.
Last year, a major IT meltdown left TSB customers without access to services and dragged on for months.