This article discusses VRRP behavior with 3 or more chassis in VRRP cluster.
When configuring VRRP with 3 or more chassis, VRRP failover randomly occurs between the other chassis and not to the next-highest-priority one.
VRRP failover uses a "first to answer" mechanism.
The chassis that answers firts will become "master" for the failover group after a failover.
To ensure that failover takes place by priority, enable preemption on chassis to ensure that the next priority chassis becomes master.
Even if another chassis answers first, preemption will ensure a failover to the highest priority chassis.