After upgrading Veeam Backup & Replication to version 12.2 and upgrading Veeam Backup for Nutanix AHV to version 6.0, jobs fail to start and the Veeam Appliance is shown as unavailable in Veeam Backup & Replication Console. Additionally, attempts to update Proxy parameters fail with errors:

Failed to edit the backup appliance settings: The backup appliance did not start within the expected time period

or

Failed to synchronize jobs: Communication channel has been forcibly closed.

When this occurs the Appliance Web-UI shows error 502.

This issue occurs because the Veeam Appliance attempts to connect to Veeam Backup & Replication addresses sequentially and waits for the connection to timeout for unreachable addresses. If multiple addresses are present, the cumulative time spent waiting for connection timeouts may exceed the service start-up timeout, causing the service to fail to start.

3. Extract the package to a folder on the Veeam Backup Server.
   
4. Close all Veeam Backup & Replication console sessions on the Veeam Backup Server.
   Process name: veeam.backup.shell.exe
5. Open Programs and Features (appwiz.cpl) and uninstall "Nutanix AHV Plugin for Veeam Backup & Replication" version 12.6.0.632.
6. From the folder where you extracted the download zip, right-click on NutanixAHVPlugin_12.6.0.636.exe and select "Run as administrator" to install the new plugin version.
7. After installing the new plugin, open the Veeam Backup & Replication console and manually create a new configuration backup.
   Be sure you know the backup file encryption password and then use 'Backup now' button to create the latest configuration.
8. If the proxy server's status is not 'Out of Date', rescan the Nutanix Clusters.
9. Right-click on the out of date proxy, and select Upgrade to upgrade proxy appliance.
10. When the proxy appliance upgrade is complete enabled jobs disabled in Step 1 and test functionality.

If you are still experiencing issues after applying the suggested steps, open a case with Veeam Support at my.veeam.com.