Mobile operator EE appeared to suffer a major outage on its 4G network yesterday, as users complained about not being able to access the internet from their mobile devices.
Users headed to Twitter and EE's subscriber forum to criticise the firm as they failed to get online with their devices.
According to the forum, EE acknowledged it had "seen an increase in customers not being able to access data".
"This is sporadic, and the majority of customers are connecting fine, but we're urgently investigating the IT issue that's causing this," said EE in a statement on the forum.
According to data collected by website Downdetector.co.uk, A sharp increase in the number of reports of problems happened around 1pm yesterday, and only started to subside at around 8pm in the evening before returning to normal around midnight. The problem affected users across the UK.
EE community manager Ed_H said the firm had identified the cause of the problem, but stopped short of revealing what it was.
"Our engineers are now at our switch sites and are working to get all of you back online as soon as possible," he said.
"Most customers seem to be OK. But for those of you still having trouble, try toggling from 4G to 3G and back again. That should move you to a new switch site from which you'll be able to get access."
One user criticised EE and said the firm appeared to be unaware of problems until users started complaining on forums.
"What I don't understand is how in 2014 you can't have some sort of monitoring system which tells you when your hardware isn't working. Instead you seem to wait until people start reporting that there is an issue. Is it not possible to have a monitoring system?" said forum user Ivanbw in a post.
EE was hit by another outage, earlier in May, that left many unable to text and make calls. Again, EE did not reveal what caused the fault.
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Rene Millman is a freelance writer and broadcaster who covers cybersecurity, AI, IoT, and the cloud. He also works as a contributing analyst at GigaOm and has previously worked as an analyst for Gartner covering the infrastructure market. He has made numerous television appearances to give his views and expertise on technology trends and companies that affect and shape our lives. You can follow Rene Millman on Twitter.