In R80.x policies of IPS,DLP, Appi,Threat Prevention... blades you will see under 'Legacy'
and these events are not relevant anymore, because the data of these blades will be displayed as log / session on "Logs&Monitor".
So all policies that under "Legacy" section have to be unchecked, except to policies for which automatic reactions configured.
When configuring automatic reactions for legacy policies check "Send automatic reactions but don't generate an event".
If you don't receive mail after checking this option, please open task to install HF that fixes the issue.