Comment 4 for bug 2052681

Alright, confirmed:
https://review.opendev.org/c/openstack/neutron/+/661760/7/neutron/agent/l3/ha_router.py#362
This line added the service param to the ProcessManager and no pid_file. Then ProcessManager build the new pid path to <router_id>.monitor.pid.neutron-keepalived-state-change-monitor.

So, IMO, after an upgrade with https://review.opendev.org/c/openstack/neutron/+/661760, many neutron external process will be re-spawned, and stale processes remain.