Opening the Operations monitor and changing to the sheet "24-Hour Summary" causes 100% CPU consumption. This can be only resolved by a service or server reboot.
Operations Monitor tries a to heavy aggregation and stalls the engine indefinitely.
There is a open Bug with R&D QLIK-92601, but still no final solution to it. As soon as you encounter this bug, we would kindly ask you to export the version of your operations monitor at the time you had the issue and open a case with Qlik Support so we can send the app to R&D. Please state the Version of Qlik Sense you are using. The issues has been spotted in version November 2017, February 2018, April 2018, June 2018.
When testing the exported apps locally we can see that up to the verison Qlik Sense November 2018 the issue is reproduceable.
After the next reload of the Operations Monitor you might not see the issue again, that is why its important to export the app right away before a new reload is triggered.
If you are running Qlik Sense April 2018 and later you can try the version 7.15.0 Operations Monitor available at https://community.qlik.com/t5/Qlik-Monitoring-Administration/Sense-Operations-Monitor/gpm-p/1578605#M8