Reason
Microsoft is rolling out a change regarding TLS 1.2 for security reasons.
Resolution
To resolve the issue, please update to the most recent Layer2 Cloud Connector version. Please follow the steps that are described here: Why and How to Update the Layer2 Cloud Connector to check whether you can just do an in-place update and whether you have the right license in place.
In case the update does not resolve the issue, please notify us by email: support@layer2solutions.com.
Furthermore, please check if TLS 1.2 is properly configured/enabled on the machine running the Cloud Connector. Various steps may be required for activation. Please refer to the following links:
https://www.layer2solutions.com/support/cloud-connector-faqs/how-to-enable-tls-1.2-on-a-cloud-connector-host-machine
https://docs.microsoft.com/en-us/sharepoint/troubleshoot/administration/authentication-errors-tls12-support
One customer has reported an issue with Cipher Suites settings that are mentioned in Microsoft's TLS article. They tried to enable the settings but the changes didn't correctly apply which wasn't clear from the beginning. If you continue to experience issues after applying Cipher Suites setting changes consider using a 3rd party tool to display active Cipher Suites and change prioritization (for example IIS Crypto from Nartac Software).