Proxmox and RouterOS 7.17 may have issues:
http://forum.mikrotik.com/t/ipv6-neighbor-discovery-broken-between-switches/181979/1
http://forum.mikrotik.com/t/chr-downgrade-on-v7/181975/1
https://forum.mikrotik.com/viewtopic.php?t=213941&hilit=Proxmox&start=300#p1125309