The company said the outage that began about 10.30pm AEDT on Tuesday was caused by an automatically generated configuration file, designed to manage potential security threats.
The file grew too large and crashed the software system handling traffic for several Cloudflare services, the company, whose network handles about a fifth of all web traffic, said.
The company said it has started to investigate and has deployed a fix but some customers might still be affected as it recovers service globally.
Its shares were down 2.3 per cent in morning trading.
Cloudflare said there was "no evidence that this was the result of an attack or caused by malicious activity".
It runs one of the world's largest networks that helps websites and apps load faster and stay online by protecting them from traffic surges and cyber attacks.
Last month, an outage at Amazon's cloud service caused global turmoil as thousands of popular websites and apps, including Snapchat and Reddit, were inaccessible due to the disruption.
The latest outage at Cloudflare prevented thousands of users from accessing platforms such as Canva, X, Grindr and ChatGPT, prompting users to log outage reports with Downdetector.
X and ChatGPT-creator OpenAI did not respond to requests for comment.
Others platforms that experienced outages included Shopify, Dropbox, Coinbase and the Moody's credit ratings service.
Moody's website displayed an Error Code 500 and instructed individuals to visit Cloudflare's website for more information.
Reports about issues with Cloudflare dropped to about 2800 by 2.20am AEDT from a peak of more than 11,000, the outage-tracking tool showed.
Downdetector tracks outages by collating status reports from a number of sources.
Since the numbers are based on user-submitted reports, the actual number of affected users may vary.
"We saw a spike in unusual traffic to one of Cloudflare's services beginning at 11:20 UTC. That caused some traffic passing through Cloudflare's network to experience errors," the company said earlier in the day.
with AP
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