Just a day after Amazon Web Services (AMZN) suffered problems at its data center in Northern Virginia, one of its customers is having connectivity problems on its own.

Slack, a popular workplace chat and collaboration platform, confirmed on its website on Wednesday afternoon that the system wasn’t working for everyone. Some users—including multiple titles at Fortune parent company Time Inc.—have not been able to access the program through the mobile and desktop apps as well as the browser portal.

Get Data Sheet, Fortune‘s technology newsletter.

“We’re currently looking into the issue that some teams are having when connecting,” read the first notice on Slack’s site at 11:27 a.m. PT/2:27 p.m. ET. “We will update this page with more information as it becomes available.”

It was followed by an update 10 minutes later that Slack “identified the root cause and are now working to fix it.”

Fortune reached out for further comment. A Slack spokesperson told Fortune that Slack was “affected by the AWS outage yesterday, but the issues should be resolved.” A second Slack spokesperson replied, “Slack is experiencing some difficulties right now, and we’re working to resolve the issue as quickly as possible.”

UPDATE: Slack issues appeared to have been resolved off and on, although the service—designed to encourage collaboration and productivity—was down for nearly an hour.

Slack said approximately 5% of its users had trouble connecting. The platform counted approximately 4 million users as of November 2016.