The XOS command vrrp-relinquish-master takes effect only if the given failover-group is master, enabled, and actual-priority is less than 255.
Trying to trigger a VRRP failover fails if current VRRP priority is 255:
CBS# show vrrp
Priority is Actual/Configured
FG-ID Priority Status Preempt Master Sys ID Master Priority
20 255/255 Master off 5 255
CBS# vrrp-relinquish-master FG
% Unrecognized command