You have 2 VMware Horizon View Connection servers with the version 5.3.2-1887719 in your environment that displays a red exclamation mark under the Last Backup column:
Hovering over the red exclamation mark displays the message:
One or more View Composer backups failed. See the event log for more details.
This apparently is a bug in version 5.3.2 build 1887719. The message will no longer appear once the connection servers are upgraded to version 6: