Thanks you The.racking.monkey for your answer,
Here is the results of the show vrrp command after the reboots of the preferred master
PREFERRED-MASTER
Virtual Router 101:
Description Preferred-Master
Admin State UP, VR State MASTER
IP Address 192.168.1.12, MAC Address 00:00:5e:00:01:65, vlan 1
Priority 110, Advertisement 1 sec, Preemption Disable Delay 0
Auth type PASSWORD, Auth data: ********
tracking type is master-up-time, duration 30 minutes, value 20
tracked priority 110
BACKUP-MASTER
Virtual Router 101:
Description Backup-Master
Admin State UP, VR State BACKUP
IP Address 192.168.1.12, MAC Address 00:00:5e:00:01:65, vlan 1
Priority 100, Advertisement 1 sec, Preemption Disable Delay 0
Auth type PASSWORD, Auth data: ********
tracking type is master-up-time, duration 30 minutes, value 20
tracked priority 100
I will try a cold boot of both controllers later in peak hours.