Generally you are right, that there is only one pvescheduler process per host. But from time to time that one pvescheduler starts a child process. That second process runs directly under the main process:
ps -eo pid,ppid,stat,lstart,etimes,cmd | awk ‘/[p]vescheduler/ {print}’
15341 1 Ss Wed Jun 24 14:26:04 2026 790521 pvescheduler
2210958 15341 S Fri Jul 3 17:59:59 2026 85 pvescheduler
If Checkmk runs at that time it counts the temporary worker and immediately triggers a CRIT alert at 2/2.
In my opinion, the Checkmk rule for this process is too restrictive. It would make more sense to check for at least one process and have no upper limit. Or at least allow two temporarily. Nearly 1.200 alarm and all-clear-e-mails in two weeks. Good, that those mails are just delivered locally.