Are you using the Delta Pull functionality?
Yes, it is configured and disabling it fixes the issue.
The performance issue is not dependent on whether the delta pull is set up or not.
CPU Spikes may occur when there is a high volume of workitems coming into the worklist. The Delta Pull mechanism should always be used in this case. So, if the delta pull mechanism is not configured, please try to set it up as per the following documentation.
Sometimes, a high CPU usage is related to the delta pull functionality. If the delta pull DB queries are slow, the system will be slow. To discard this possibility, try to switch off the delta pull for the BPM tasks. You need to set the "Delta Pull channel refresh period (seconds) to -1"
This way the Delta Pull will be disabled. Keep in mind that the UWL users will have to refresh the inbox manually once the delta pull functionality is disabled.