Issue looks to be fixed in rolling version you've stated. Reboot now immediate without any hang. Thanks.

I'm also experiencing this for the latest rolling versions eg. https://downloads.vyos.io/rolling/current/amd64/vyos-1.3-rolling-201912181733-amd64.iso. This is causing issues when trying to create Packer image builds - total first reboot wait time extended to over 2mins for a successful image build.