The world's most popular messaging app suffered 6,236 hours of disruption in 2019, according to the study by Top10VPN, with countries like Sri Lanka and Sudan among the worst affected.
Samuel Woodhams, digital rights expert and co-author of the report, said WhatsApp's end-to-end encryption and vast user base makes it an ideal platform for evading authorities during periods of civil unrest.
"Shutting it down makes it near-impossible for people to communicate in these situations, making it easier for authorities to maintain their grip on power," he told The Independent.
"It's frighteningly easy for authoritarian governments to shutdown platforms like WhatsApp, or even internet access as a whole... They rely on government licenses and so are forced to comply with governement demands in order to continue operating in that country."
Other platforms to face significant disruption last year include Facebook, Twitter and YouTube.
The study estimated that the economic cost of internet shutdowns globally was more than $8 billion (£6bn), caused by 122 major shutdowns across 21 countries.
The most heavily-impacted nation was Iraq, followed by Sudan, India, Venezuela and Iran. Shutdowns generally came in response to protests or civil unrest, especially in the build-up to elections.
"We found that there were more internet shutdowns in 2019 than ever before," the report stated. "We calculated over 18,000 hours of internet shutdowns around the world in 2019, [representing] a 235 per cent increase compared to 2015/16."
Beyond the economic impact, the researchers said the shutdowns were especially worrying for human rights and democracy.
However, not all shutdowns were an attempt to stifle free speech. In India last August, internet connections were blocked in an attempt to "prevent rumour-mongering" and the spread of misinformation that led to violent protests in some areas of the country.
A spokesperson for WhatsApp said at the time: "The challenge of mob violence requires government, civil society, and technology companies to work together. The police also use WhatsApp to discuss investigations and report crimes."
WhatsApp did not immediately respond to a request for comment on the latest research.
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