What would be the most plausible reason why?

C
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Adding Processing Cores to the Hardware
Increasing the number of processing cores on the hardware platform does not automatically increase the number of kernel instances. If the number of kernel instances is not increased, CoreXL does not utilize some of the processing cores. After upgrading the hardware, increase the number of kernel instances using cpconfig.

Reinstalling the gateway will change the number of kernel instances if you have upgraded the hardware to an increased number of processing cores, or if the number of processing cores stays the same but the number of kernel instances was previously manually changed from the default. Use cpconfig to reconfigure the number of kernel instances.

In a clustered deployment, changing the number of kernel instances (such as by reinstalling CoreXL) should be treated as a version upgrade. Follow the instructions in the R76 Installation and Upgrade Guide, in the “Upgrading ClusterXL Deployments” chapter, and perform either a Minimal Effort Upgrade (using network downtime) or a Zero Downtime Upgrade (no downtime, but active connections may be lost), substituting the instance number change for the version upgrade in the procedure. A Full Connectivity Upgrade cannot be performed when changing the number of kernel instances in a clustered environment.

C. run cpconfig to increase the firewall instances.