One of my ESXis went offline after hardware failure, after fixing it, the red alert triangle appeared on all VMs, and there is no way to clear it, this is if I am logged in through the vCenter, BUT there were no alerts if you login directly to ESXi.
Solution:
From the vCenter, click on the ESXi host "Configuration" tab, select "Security Profile", then from Services properties I have restarted VPXA services which is vCenter account on the ESXi, I lost connection to ESXi host temporary but it recovered after "Reconnect" and the alerts cleared!