Does Transit Routing inside a hub VCN work on an upgraded DRG?

Summary:

We have an upgraded DRG and I'm trying to set up VPN access

Content (required):

I'm following the instructions given here: https://docs.oracle.com/en-us/iaas/Content/Network/Tasks/transitrouting.htm

Which almost worked, but was constantly losing the connection to one or more of the VCNs. I would be unable to connect to one of the VCNs from my workstation across the VPN connection, whilst still able to connect to other VCNs. These connections were completely unstable with the connections dropping and re-connecting. Once up the connection might remain stable for a few minutes up to a couple of hours, but then would drop again. It would remain disconnected for a few minutes up to a couple of hours.