How do you acknowledge multiple alerts via console?

On the alerts page you can click on the check boxes for each alerts you want to ACK then click on the top Acknowledge link. You can also filter the alert list to just the ones you want to ACK (like searching for "Uptime") then click on the top checkbox to select all that match your filter before clicking on Acknowledge.

"System Uptime" (WinSystemUptime) will typically just alert for the first hour (3600sec) when a Windows system reboots then auto-clears itself. When you do maintenance/patching or have expected downtime, it's suggested you setup a SDT ahead of time so you don't get notifications for expected alerts.