Hey,
I have been in touch with our Cisco Partner about this, but I didn't get anywhere and the case was closed without a resolution..
It turns out that you cannot clear more than 1000 alerts at once in ISE.
This is a huge issue for me, because we have over 10k configuration change alerts that was generated when a user mistakenly created a few too many guest accounts through the sponsor portal.
I am hoping there is a way I can clear up all these old alerts without having to click 9k of them one at a time to clear them..
I considered automating the clicking through javascript in my browser, but of course the alert list was a flash object, so I couldn't do that either..
-- Regards, Morten