It is derived from ZBX-20030.
After having fixed of ZBX-20030, CPU count has no problem when add CPUs using CPU hot-plugging.We could get correct number of CPU cores using system.cpu.num key on Windows OS where is running zabbix-agent2.
But our customer found that when add CPUs using CPU hot-pluggin, only could get correct value after restarting service of zabbix-agent2 ,using system.cpu.load key on Windows OS,while agent1 works all fine

Steps to reproduce:
Environment:
OS: Windows Server 2012R2 (on VMware ESXi 6.7)
HotAdd CPU cores from 2 to 4（using VMware vCenter GUI）

7/4 14:55　(before HotAdd, CPU:2cores)
agent2: system.cpu.load[percpu,avg1]=0.55, system.cpu.load[all,avg1]=1.13
agent1: system.cpu.load[percpu,avg1]=1.35, system.cpu.load[all,avg1]=2.71

7/4 15:05　(after HotAdd, CPU:4cores)
agent2: system.cpu.load[percpu,avg1]=1.11, system.cpu.load[all,avg1]=2.23
agent1: system.cpu.load[percpu,avg1]=0.84, system.cpu.load[all,avg1]=3.35

7/4 16:05　(after restarting zabbix-agent2)
agent2: system.cpu.load[percpu,avg1]=0.22, system.cpu.load[all,avg1]=0.88
agent1: system.cpu.load[percpu,avg1]=1.83, system.cpu.load[all,avg1]=7.3

Please also refer to below graphs,