Hi Egert,
Just going by the log provided from the switch, its pretty interesting that the switch sees the VRRP packet as an IPsec packet and tries to decapsulate it in which it fails.
1. this is a VRRP packet destined to 224.0.0.18 so it should just switch it unless it is also running VRRP.
2. The IP protocol found by the switch seems to be "prot=51" which is for AH. the VRRP packet should have ip proto 112 in it.
Just took a quick packet capture on one of the vSRXs in my lab and i could see it using the correct protocol number in the VRRP packet.
wonder if the packet is getting read incorrectly by the intermediate device in question.
Let us know if you find out the solution. it does not appear to be VRRP device issue.
Thanks,
Kinshuk