Downdetector, which tracks internet outages, was showing significant spikes at both Slack and Amazon Web Services, although Amazon repeatedly denied to Fortune that it suffered a widespread outage. Slack acknowledged the outage on its website’s status page, saying, “We’re investigating the issue where Slack is not loading for some users. We’re looking into the cause and will provide more information as soon as it’s available.”

As of 12:07 p.m. ET, the company added it was starting to see “signs of improvement” but was “still monitoring the situation. Amazon said that despite AWS outages appearing on Downdetector as of 12:23 p.m. ET, its own service health dashboard showed that AWS was not, in fact, down.

Slack also experienced a separate outage for some customers the previous night at approximately 8 p.m. ET, but said that issue had been resolved at 9:48 p.m. ET.

The popular messaging service has more than 156,000 paying corporate customers (including Fortune). That number jumped 42% in the past year, as more and more companies rely on it with a significant portion of their employee base working remotely.

The outage, predictably, resulted in a number of internet reactions, largely sarcastic.

The outage is a boon for Microsoft Teams, Slack’s biggest rival, which was not reporting notable outages Monday morning.

Any outage at AWS did not seem to be having the cascading effects that were seen last December. That outage, caused by a software problem, affected everything from Disney amusement parks and Netflix videos to robot vacuums and Adele ticket sales.

Luke Deryckx, the CTO of Downdetector’s parent company Ookla, told TechRadar on Wednesday, “We see a small number of credible reports that some AWS users had issues with their platform yesterday. However, we do not believe there was a widespread service issue on AWS’s platform. To put it in context, Downdetector received about 8,000 total user reports of problems at AWS yesterday, whereas we received over 400,000 user reports during the most recent significant AWS outage on December 16.”

An AWS spokesperson told Fortune, “there was no broad service issue with AWS. Our services were operating normally. The only resource on the internet that provides accurate data on the availability of our services is the AWS Service Health Dashboard.”

[This report has been updated to clarify how Downdetector could show reports of outages on AWS but the AWS Service Health Dashboard did not.]