Troubleshooting – Backup Failed? Snapshot Failed? Agent communication Failed?

You may receive "VM Agent unable to communicate with Azure Backup/ VMSnapshot extension operation failed” when protecting your IAAS Virtual Machines using Azure Backup. Most of the Azure Backup failures that we encounter at support are due to the VM agent is unable to communicate with the Azure Backup Service.", "Snapshot operation failed due to no network connectivity on the virtual machine.  

This https://docs.microsoft.com/en-us/azure/backup/backup-azure-troubleshoot-vm-backup-fails-snapshot-timeout#summary details some of the more common error messages encountered, along with troubleshooting steps to resolve them.