After the update from 2.346.1 to 2.346.2 (including all plugins at that time) the libvirt plugin stopped working for me.

Problems:

• The slave configuration is accessible but I cannot see/select any hypervisor
• There is a "Uncategorized/libvirt" section in the /manage menu
  • The icons are not loaded (404 error)
  • There are no hypervisors
  • No option to edit or create hypervisors
• The "Cloud" section in "Manage Jenkins" mentioned by the documentation is gone

What I did:

1. Tried to build a project using the plugin that last succeeded on 28. June with Jenkins 2.346.1
2. Failed because the agent did not start
3. Checked the slave config page and hypervisor was selectable  but no snapshots
4. Hypervisor was listed under "Uncategorized/libvirt" but I could not see any config
5. Disabled the plugin and restarted Jenkins
6. Enabled the plugin again and restarted Jenkins
7. Hypervisor is gone
8. I could not find any error messages in the Jenkins log 
9. Slave config page says "ERROR: Could not find our libvirt cloud instance!"

Additional information:

On 23. June I upgraded from 2.319.2 to 2.346.1 and on 28. June the last build was done.

I always update the Jenkins plugins along with the apt updates.