If snapshot in VMware (5.5) is requested with "quiesce file system" VyOS freezes (Can't login to console/ssh, openvpn stops working, general routing/forwarding is not affected). This is default behaviour of Veeam 7 during backup jobs.
According to https://github.com/vmware/open-vm-tools/issues/16 , problem is caused by broken open-vm-tools / ESXi / kernel. It was already fixed in open-vm-tools.
open-vm-tools 9.4.* seems to be affected, uprgrading to 9.10 should fix this.
VyOS 1.1.6 and 1.1.7 affected.
VC6.5R1 is not affected (Using open-vm-tools 8.*)