Microsoft is actively addressing a service degradation issue affecting Microsoft Teams users worldwide. Upon launching the desktop or web application, users are met with a couldn’t connect to this app error message, hindering access to the platform. This problem, identified as TM1131505, originated from a recent update aimed at enhancing the user interface, particularly the left-hand navigation sidebar.
Incident Overview
The issue surfaced on August 8, 2025, when users began reporting difficulties accessing Microsoft Teams. The error message appears during the application’s startup sequence, preventing it from loading correctly. Microsoft’s investigation revealed that the root cause was an unoptimized code flow introduced during the sidebar enhancement update. This unintended code path led to the connection error, impacting a broad spectrum of users across various organizations.
Temporary Workaround
To mitigate the disruption, Microsoft has provided a simple workaround. Affected users can bypass the error screen by clicking on the Activity or Chat icons located in the left-hand navigation sidebar. This action successfully loads the application, restoring access to all functionalities. While this solution is effective, it is a temporary measure until a permanent fix is fully deployed.
Deployment of the Fix
As of August 19, 2025, Microsoft announced that the deployment of the corrective patch is well underway, with approximately 25% of the global infrastructure having received the fix. The company anticipates completing the deployment and fully resolving the issue by the next scheduled communication on August 21, 2025, at 6:30 PM UTC. Microsoft has classified the impact as a service degradation, indicating that the core service remains operational despite the disruptive bug. Importantly, this is not a security-related incident, and user data remains secure.
Additional Troubleshooting Steps
In addition to the provided workaround, users can take several steps to address the couldn’t connect error:
1. Check Internet Connection: Ensure that your internet connection is stable. A weak or unstable connection can lead to connectivity issues with Microsoft Teams. Switching between Wi-Fi and a wired connection may help determine if the network is the cause.
2. Clear Teams Cache: Corrupted cache files can cause connectivity problems. To clear the Teams cache:
– Close Microsoft Teams.
– Press `Win + R` to open the Run dialog box.
– Type `%appdata%\Microsoft\Teams` and press Enter.
– Delete all files and folders within the directory.
– Restart Microsoft Teams.
3. Update Microsoft Teams: Running an outdated version of Teams can lead to issues. To update:
– Open Microsoft Teams.
– Click on your profile picture in the top-right corner.
– Select Check for updates.
– Teams will automatically download and install any available updates.
4. Adjust Firewall and Security Settings: Firewalls and antivirus software can sometimes block Microsoft Teams from accessing the internet. Ensure that Teams is allowed through your firewall and antivirus settings. You may need to consult your IT department or antivirus documentation for specific instructions.
5. Disable Proxy Settings (If Applicable): Proxy servers and network settings configured on your device can sometimes interfere with Teams’ ability to connect. Adjusting proxy settings or bypassing proxies for Teams traffic may help resolve connectivity issues.
6. Reinstall Microsoft Teams: If other methods fail, reinstalling Teams can resolve deeper software issues.
– Uninstall Microsoft Teams from your device.
– Download the latest version from the official Microsoft website.
– Install the application and sign in with your credentials.
Security Advisory
In a related development, Microsoft disclosed a critical remote code execution (RCE) vulnerability in its Teams collaboration software as part of the August 2025 Patch Tuesday updates. The flaw, identified as CVE-2025-53783, could allow an unauthorized attacker to read, write, and delete user messages and data by executing code over a network. Users are strongly advised to apply the latest security patches to mitigate this risk.
Conclusion
Microsoft is committed to resolving the couldn’t connect error affecting Teams users and is making significant progress in deploying a permanent fix. In the interim, users can utilize the provided workaround and follow additional troubleshooting steps to maintain access to their Teams environment. Staying informed through official Microsoft communications and applying necessary updates will ensure a secure and efficient collaboration experience.
