Just an FYI to others, but I have dual MX setup (primary/warm-spare) and I use a VIP on both my WAN1 (DIA) and WAN2 (MG51 cellular) connections.
VIP function works on 18.107.2, but upgraded to 18.207 and VIP function stopped working.
Only noticed because I happen to be running PCAPs to test something else, but also confirmed via ARP table on MG51 not showing the VIP anymore. Downgraded, and PCAPs and ARP both showing correctly.