EXOS has the limitation of 7 virtual MAC addresses for VRRP until 16.1. After 16.2 the limit is 31 addresses.
The VRRP MAC address for an IPv6 VRRP router instance is an IEEE 802 MAC address in the following hexadecimal format (in Internet-standard bit-order): 00-00-5E-00-02-<vrid>
This way even when less than 7 VRIDs are created, possibly the limit of MAC addresses can be surpassed.
MAC for IPv4 VRRP VRID 1: 00:00:5e:00:01:01
MAC for IPv6 VRRP VRID 1: 00:00:5e:00:02:01
This causes the switch to possibly not have the correct entries in hardware and therefore the switch does not forward VRRP hellos on some VLANs to the CPU, causing this dual-mastership on certain VLANs.