This article explains how to fix the issue when you upgrade the device QFX5120-32C from 22.2R3.15 to 23.4R2-S4.11 and not receiving the VRRP IPv6 packets.

• All servers are configured with Keepalived using VRRP over IPv6 in customer environment. When the QFX5120-32C switch is running Junos OS version 22.2R3.15, the servers are able to communicate, send production traffic, and exchange VRRP IPv6 packets without issue. However, after upgrading the switch to version 23.4R2-S4.11 without any configuration changes, VRRP IPv6 packets are no longer observed.
• It was observed that IGMP snooping is enabled globally for all VLANs.

Issue was resolved after disabling protocols igmp-snooping vlan all. This appears to be related to changes in IGMP snooping behavior in the newer Junos version interacting with VRRPv3. As per below article, VRRPv3 advertisements are not forwarded on a Layer 2 VLAN on which IGMP snooping is enabled. The workaround is to "disable igmp-snooping".

https://supportportal.juniper.net/s/article/EX-How-to-configure-verify-and-troubleshoot-VRRP-V3-on-EX-Switches?language=en_US

https://supportportal.juniper.net/s/article/EX-How-to-configure-verify-and-troubleshoot-VRRP-V3-on-EX-Switches?language=en_US