The problem has persisted since 9 a.m. and mainly affects people in the UK, according to the DownDetector website.
The Silicon Valley-based tech company has yet to recognize the issue, which has been widely discussed online.
Social media users said they were unable to attend meetings and reported having audio problems during calls. Connection problems have also been reported.
At 4 p.m. Sunday, approximately 1,400 unresolved issues were reported to the service.
Video conferencing software quickly gained popularity during the coronavirus pandemic as millions of people turn to its group video calling features to work and study at home.
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The company said last month it had about 300 million attendees in daily meetings, up from 10 million in December.
The platform has come under scrutiny over a number of security concerns, including the practice known as “Zoombombing” where strangers enter group discussions and show other participants of the explicit material.
Concerns about the use of the Zoom video app are “normal speed bumps” in the rise of a new service, said a senior executive at the firm.
Earlier this month, a church said a hacker had broken into his virtual Bible study and released porn during the class.
The Smutty content was played during a Zoom call hosted by the Saint Paulus Lutheran Church in San Francisco on May 6.
Elderly parishioners were forced to watch the X-rated video, leaving them “traumatized and helpless,” says a lawsuit filed on behalf of the church.
St Paulus is now suing the Zoom video streaming service for failing to provide adequate protection to prevent the hacker from entering.